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date [-d @int|str] [+%s|"+%F %T"]
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dancing links code 6-7

六、pku 3074
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#include<stdio.h>
#include<algorithm>
#include<math.h>
#include<string.h>

using namespace std;

const int MAXN = 1005;
int L[MAXN*MAXN], R[MAXN*MAXN], U[MAXN*MAXN], D[MAXN*MAXN];
int S[MAXN];
int Col[MAXN*MAXN], Row[MAXN*MAXN],Ans[MAXN],ans,limit,up;

void Remove(int c) {
	L[R[c]] = L[c];
	R[L[c]] = R[c];
	for (int i = D[c]; i != c; i = D[i])
		for (int j = R[i]; j != i; j = R[j]) {
			U[D[j]] = U[j];
			D[U[j]] = D[j];
			-- S[Col[j]];
		}
}

void Resume(int c) {
	for (int i = U[c]; i != c; i = U[i])
		for (int j = L[i]; j != i; j = L[j]) {
			U[D[j]] = j;
			D[U[j]] = j;
			++ S[Col[j]];
		}
	L[R[c]] = c;
	R[L[c]] = c;
}

bool dfs(int depth) {
	if(R[0] == 0) { if(depth > ans)ans = depth; return true; }
	int i, j, c, minnum = 1000000000;
	for (i = R[0]; i != 0; i = R[i]) {
		if (S[i] < minnum) {
			minnum = S[i];
			c = i;
		}
	}
	Remove(c);
	for (i = U[c]; i != c; i = U[i]) {
		Ans[depth] = Row[i];
		for (j = R[i]; j != i; j = R[j]) Remove(Col[j]);
		if (dfs(depth + 1)) return true;
		for (j = L[i]; j != i; j = L[j]) Resume(Col[j]);
	}
	Resume(c);
	return false;
}

int solve(int n, int m, int DL[][MAXN]) {
	for (int i = 0; i <= m; i ++) {
		L[i] = i - 1;
		R[i] = i + 1;
		U[i] = D[i] = i;
	}
	L[0] = m;
	R[m] = 0;
	int cnt = m + 1;
	memset(S, 0, sizeof (S));
	for (int i = 1; i <= n; i ++) {
		int head = cnt, tail = cnt;
		for (int c = 1; c <= m; c ++) if (DL[i][c]) {
			S[c] ++;
			Row[cnt] = i;
			Col[cnt] = c;
			U[D[c]] = cnt;
			D[cnt] = D[c];
			U[cnt] = c;
			D[c] = cnt;
			L[cnt] = tail;
			R[tail] = cnt;
			R[cnt] = head;
			L[head] = cnt;
			tail = cnt;
			cnt ++;
		}
	}
	if (dfs(0)) return true;
	return false;
}

int mark[MAXN][MAXN],x[MAXN],y[MAXN],z[MAXN];

int main()
{
	int i,j,k,l,n,m,T,boo,row,col,a[33][33],low,ok1[13][13],ok2[13][13],ok3[13][13],x1,y1,ii,jj;
	int id1[13][13],id2[13][13],id3[13][13],ok[13][13][13];
 
	char ch[999];
	while(scanf("%s",ch) != EOF && strcmp(ch,"end") != 0)
	{
		k = 0;
		for(i=1;i<=9;i++)
			for(j=1;j<=9;j++)
			{
				if(ch[k] != '.') a[i][j] = ch[k] - '0'; else a[i][j] = -1; k++;
			}
  
  
		for(i=1;i<=9;i++)
			for(j=1;j<=9;j++)
			if(a[i][j] == -1)
				for(k=1;k<=9;k++)
				{
					boo = 1;
					for(l=1;l<=9;l++)if(a[l][j] == k)boo = 0;
					for(l=1;l<=9;l++)if(a[i][l] == k)boo = 0;
					x1 = (i-1)/3*3+1; y1 = (j-1)/3*3+1;
	 
					for(ii=x1;ii<x1+3;ii++)
						for(jj=y1;jj<y1+3;jj++)
						if(a[ii][jj] == k)boo = 0;
	 
					ok[i][j][k] = boo;
				}
  
		row = 0; col = 0;
		for(j=1;j<=9;j++)
			for(k=1;k<=9;k++)
			{
				boo = 1;
				for(i=1;i<=9;i++)if(a[i][j] == k)boo = 0;
				if(boo == 1)
				{
					col++; id1[j][k] = col;
				}
				else
					id1[j][k] = -1;
			}
  
		for(i=1;i<=9;i++)
			for(k=1;k<=9;k++)
			{
				boo = 1;
				for(j=1;j<=9;j++)if(a[i][j] == k)boo = 0;
				if(boo == 1)
				{
					col++; id2[i][k] = col;
				}
				else
					id2[i][k] = -1;
			}
   
		for(i=1;i<=9;i++)
		{
			x1 = (i-1)/3*3+1; y1 = (i-1)%3*3+1;
			for(k=1;k<=9;k++)
			{
				boo = 1;
				for(ii=x1;ii<x1+3;ii++)
					for(jj=y1;jj<y1+3;jj++)
					if(a[ii][jj] == k)boo = 0;
				if(boo == 1)
				{
					col++; id3[i][k] = col;
				}
				else id3[i][k] = -1;
			}
		}
  
		for(i=1;i<=9;i++)
			for(j=1;j<=9;j++)
			if(a[i][j] == -1)
				for(k=1;k<=9;k++)
				if(ok[i][j][k] == 1)
				{
					row++; x[row] = i-1; y[row] = j-1; z[row] = k;
					for(ii=1;ii<=col;ii++)mark[row][ii] = 0;
	 
					mark[row][id1[j][k]] = 1;
					mark[row][id2[i][k]] = 1;
					mark[row][id3[(i-1)/3*3+(j-1)/3+1][k]] = 1;
				}
  
		int rr=0;
		for(i=1;i<=9;i++)
			for(j=1;j<=9;j++)
			if(a[i][j] == -1)
			{
				col++; for(k=1;k<=row;k++)mark[k][col] = 0;
				for(k=1;k<=9;k++)
				if(ok[i][j][k] == 1)
				{
					rr++; mark[rr][col] = 1;
				}
			}
 
		ans = 0;
		k = solve(row, col, mark);
   
		for(i=0;i<ans;i++)
		{
			ch[x[Ans[i]]*9+y[Ans[i]]] = z[Ans[i]] + 48;
		}
		printf("%s\n",ch);
  
	}
	return 0;
}

七、pku 3076
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#include<stdio.h>
#include<algorithm>
#include<math.h>
#include<string.h>

using namespace std;

const int MAXN = 2005;
int L[MAXN*MAXN], R[MAXN*MAXN], U[MAXN*MAXN], D[MAXN*MAXN];
int S[MAXN];
int Col[MAXN*MAXN], Row[MAXN*MAXN],Ans[MAXN],ans,limit,up;


void Remove(int c) {
	L[R[c]] = L[c];
	R[L[c]] = R[c];
	for (int i = D[c]; i != c; i = D[i])
		for (int j = R[i]; j != i; j = R[j]) {
			U[D[j]] = U[j];
			D[U[j]] = D[j];
			-- S[Col[j]];
		}
}

void Resume(int c) {
	for (int i = U[c]; i != c; i = U[i])
		for (int j = L[i]; j != i; j = L[j]) {
			U[D[j]] = j;
			D[U[j]] = j;
			++ S[Col[j]];
		}
	L[R[c]] = c;
	R[L[c]] = c;
}

bool dfs(int depth) {
	// printf("ddd = %d  R0 = %d\n",depth,R[0]);
	if(R[0] == 0) { if(depth > ans)ans = depth; return true; }
	int i, j, c, minnum = 1000000000;
	for (i = R[0]; i != 0; i = R[i]) {
		if (S[i] < minnum) {
			minnum = S[i];
			c = i;
		}
	}
	Remove(c);
	for (i = U[c]; i != c; i = U[i]) {
		Ans[depth] = Row[i];
		for (j = R[i]; j != i; j = R[j]) Remove(Col[j]);
		if (dfs(depth + 1)) return true;
		for (j = L[i]; j != i; j = L[j]) Resume(Col[j]);
	}
	Resume(c);
	return false;
}

int solve(int n, int m, int DL[][MAXN]) {
	for (int i = 0; i <= m; i ++) {
		L[i] = i - 1;
		R[i] = i + 1;
		U[i] = D[i] = i;
	}
	L[0] = m;
	R[m] = 0;
	int cnt = m + 1;
	memset(S, 0, sizeof (S));
	for (int i = 1; i <= n; i ++) {
		int head = cnt, tail = cnt;
		for (int c = 1; c <= m; c ++) if (DL[i][c]) {
			S[c] ++;
			Row[cnt] = i;
			Col[cnt] = c;
			U[D[c]] = cnt;
			D[cnt] = D[c];
			U[cnt] = c;
			D[c] = cnt;
			L[cnt] = tail;
			R[tail] = cnt;
			R[cnt] = head;
			L[head] = cnt;
			tail = cnt;
			cnt ++;
		}
	}
	if (dfs(0)) return true;
	return false;
}


int mark[MAXN][MAXN],x[MAXN],y[MAXN],z[MAXN];
int id1[33][33],id2[33][33],id3[33][33],ok[33][33][33];

int main()
{
	int i,j,k,l,n,m,T,boo,row,col,a[33][33],low,ok1[33][33],ok2[33][33],ok3[33][33],x1,y1,ii,jj;
 
	char ch[999],cas=0;
	while(scanf("%s",ch) != EOF)
	{
		cas++; if(cas > 1)printf("\n");
		k = 16;
		for(i=1;i<16;i++)
		{
			scanf("%s",ch+k);
			k += 16;
		}//printf("safdsadfsdf\n");

		k = 0;
		for(i=1;i<=16;i++)
			for(j=1;j<=16;j++)
			{
				if(ch[k] != '-') a[i][j] = ch[k] - 'A'+1; else a[i][j] = -1; k++;
			}
  
		for(i=1;i<=16;i++)
			for(j=1;j<=16;j++)
			if(a[i][j] == -1)
				for(k=1;k<=16;k++)
				{
					boo = 1;
					for(l=1;l<=16;l++)if(a[l][j] == k)boo = 0;
					for(l=1;l<=16;l++)if(a[i][l] == k)boo = 0;
					x1 = (i-1)/4*4+1; y1 = (j-1)/4*4+1;
	 
					for(ii=x1;ii<x1+4;ii++)
						for(jj=y1;jj<y1+4;jj++)
						if(a[ii][jj] == k)boo = 0;
	 
					ok[i][j][k] = boo;
				}
  
		row = 0; col = 0;
		for(j=1;j<=16;j++)
			for(k=1;k<=16;k++)
			{
				boo = 1;
				for(i=1;i<=16;i++)if(a[i][j] == k)boo = 0;
				if(boo == 1)
				{
					col++; id1[j][k] = col;
				}
				else
					id1[j][k] = -1;
			}
 
		for(i=1;i<=16;i++)
			for(k=1;k<=16;k++)
			{
				boo = 1;
				for(j=1;j<=16;j++)if(a[i][j] == k)boo = 0;
				if(boo == 1)
				{
					col++; id2[i][k] = col;
				}
				else
					id2[i][k] = -1;
			}
   
		for(i=1;i<=16;i++)
		{
			x1 = (i-1)/4*4+1; y1 = (i-1)%4*4+1;
			for(k=1;k<=16;k++)
			{
				boo = 1;
				for(ii=x1;ii<x1+4;ii++)
					for(jj=y1;jj<y1+4;jj++)
					if(a[ii][jj] == k)boo = 0;
				if(boo == 1)
				{
					col++; id3[i][k] = col;
				}
				else id3[i][k] = -1;
			}
		}
  
		for(i=1;i<=16;i++)
			for(j=1;j<=16;j++)
		if(a[i][j] == -1)
			for(k=1;k<=16;k++)
		if(ok[i][j][k] == 1)
		{
			row++; x[row] = i-1; y[row] = j-1; z[row] = k;
			//if(i == 1 && j == 7 && k == 4)printf("row ===== %d\n",row);
			for(ii=1;ii<=col;ii++)mark[row][ii] = 0;
	 
			mark[row][id1[j][k]] = 1;
			mark[row][id2[i][k]] = 1;
			mark[row][id3[(i-1)/4*4+(j-1)/4+1][k]] = 1;
		}
  
		int rr=0;
		for(i=1;i<=16;i++)
			for(j=1;j<=16;j++)
			if(a[i][j] == -1)
			{
				col++; for(k=1;k<=row;k++)mark[k][col] = 0;
				for(k=1;k<=16;k++)
				if(ok[i][j][k] == 1)
				{
					rr++; mark[rr][col] = 1;
				}
			}
  
  
		//printf("%d %d\n",row,col);
		//freopen("out.txt","w",stdout);
  
	/* for(i=1;i<=row;i++)
		{
			printf("%d %d %d   ",x[i],y[i],z[i]);
			for(j=1;j<=col;j++)
			printf("%d ",mark[i][j]);
			printf("\n");
		}*/
		//fclose(stdout);
  
		ans = 0;
		k = solve(row, col, mark);
 
	// printf("%d k = %d %d %d\n",ans,id1[7][4],id2[1][4],id3[3][4]);
  
		for(i=0;i<ans;i++)
		{
		// printf("%d   %d %d %d\n",Ans[i],x[Ans[i]],y[Ans[i]],z[Ans[i]]);
			ch[x[Ans[i]]*16+y[Ans[i]]] = z[Ans[i]] + 'A'-1;
		}
		//printf("\n");*/
  
		for(i=0;i<16*16;i++)
		{
			printf("%c",ch[i]);
			if(i!=0 && (i+1)%16 == 0)printf("\n");
		}
	}
	return 0;
}

dancing links code 4-5

四、hdu 3663
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#include<stdio.h>
#include<algorithm>
#include<math.h>
#include<string.h>

using namespace std;

int n,m,DD,a[66][66],s[66],f[66],id[66][6];

const int MAXN = 1005;

int L[MAXN*MAXN], R[MAXN*MAXN], U[MAXN*MAXN], D[MAXN*MAXN];
int S[MAXN];
int Col[MAXN*MAXN], Row[MAXN*MAXN],Ans[MAXN],ans,limit,up;


void Remove(int c) {
	L[R[c]] = L[c];
	R[L[c]] = R[c];
	for (int i = D[c]; i != c; i = D[i])
	for (int j = R[i]; j != i; j = R[j]) {
	    U[D[j]] = U[j];
	    D[U[j]] = D[j];
	    -- S[Col[j]];
	}
}
void Resume(int c) {
	for (int i = U[c]; i != c; i = U[i])
	for (int j = L[i]; j != i; j = L[j]) {
	    U[D[j]] = j;
	    D[U[j]] = j;
	    ++ S[Col[j]];
	}
	L[R[c]] = c;
	R[L[c]] = c;
}

bool dfs(int depth) {
//    printf("ddd = %d  R0 = %d\n",depth,R[0]);
	if(R[0] == 0) { if(depth > ans)ans = depth; return true; }
	int i, j, c, minnum = 1000000000;
	for (i = R[0]; i != 0; i = R[i]) {
	    if (S[i] < minnum) {
	        minnum = S[i];
	        c = i;
	    }
	}
	Remove(c);
	for (i = U[c]; i != c; i = U[i]) {
	    Ans[depth] = Row[i];
	    for (j = R[i]; j != i; j = R[j]) Remove(Col[j]);
	    if (dfs(depth + 1)) return true;
	    for (j = L[i]; j != i; j = L[j]) Resume(Col[j]);
	}
	Resume(c);
	return false;
}
int solve(int n, int m, int DL[][MAXN]) {
	for (int i = 0; i <= m; i ++) {
	    L[i] = i - 1;
	    R[i] = i + 1;
	    U[i] = D[i] = i;
	}
	L[0] = m;
	R[m] = 0;
	int cnt = m + 1;
	memset(S, 0, sizeof (S));
	for (int i = 1; i <= n; i ++) {
	    int head = cnt, tail = cnt;
	    for (int c = 1; c <= m; c ++) if (DL[i][c]) {
	        S[c] ++;
	        Row[cnt] = i;
	        Col[cnt] = c;
	        U[D[c]] = cnt;
	        D[cnt] = D[c];
	        U[cnt] = c;
	        D[c] = cnt;
	        L[cnt] = tail;
	        R[tail] = cnt;
	        R[cnt] = head;
	        L[head] = cnt;
	        tail = cnt;
	        cnt ++;
	    }
	}
	if (dfs(0)) return true;
	return false;
}


int mark[MAXN][MAXN],x[MAXN],y[MAXN],z[MAXN];

int main()
{
	int i,j,k,l,row,col,g;
	while(scanf("%d %d %d",&n,&m,&DD) != EOF)
	{
	    for(i=1;i<=n;i++)
	        for(j=1;j<=n;j++)
	        {
	            a[i][j] = 0;
	            if(i == j)a[i][j] = 1;
	        }
	    while(m--) {
	        scanf("%d %d",&j,&k);
	        a[j][k] = a[k][j] = 1;
	    }
	    for(i=1;i<=n;i++)scanf("%d %d",&s[i],&f[i]);
	   
	    col = 0;
	    for(i=1;i<=n;i++)
	        for(j=1;j<=DD;j++)
	            id[i][j] = ++col;
	   
	    row = 0;
	    for(i=1;i<=n;i++)
	    {
	        for(j=s[i];j<=f[i];j++)
	            for(k=j;k<=f[i];k++)
	            {
	                row++; x[row] = j; y[row] = k; z[row] = i;
	                for(l=1;l<=col;l++)mark[row][l] = 0;
	               
	                for(l=1;l<=n;l++)if(a[i][l] == 1)
	                {
	                    for(g=j;g<=k;g++) mark[row][id[l][g]] = 1;
	                }
	            }
	    }
	   
	    int rr=0;
	   
	    for(i=1;i<=n;i++)
	    {
	        col++;
	        for(j=1;j<=row;j++)mark[j][col] = 0;
	       
	        for(j=s[i];j<=f[i];j++)
	            for(k=j;k<=f[i];k++)
	            {
	                rr++;
	                mark[rr][col] = 1;
	            }
	    }
	   
	    int TT = row;
	    for(i=1;i<=n;i++)
	    {
	        row++;
	        for(j=1;j<=col;j++)mark[row][j] = 0;
	        mark[row][col-n+i] = 1;
	    }
	   
	    ans = 0;
	   
	    k = solve(row, col, mark);
	   
	    if(k == 0)
	        printf("No solution\n");
	    else
	    {
	        for(i=1;i<=n;i++)s[i] = f[i] = 0;
	        for(i=0;i<ans;i++)
	        if(Ans[i] <= TT)
	        {
	            s[z[Ans[i]]] = x[Ans[i]];
	            f[z[Ans[i]]] = y[Ans[i]];
	        }
	        for(i=1;i<=n;i++)printf("%d %d\n",s[i],f[i]);
	    }
	    printf("\n");
	}
	return 0;
}
五、hdu 2995
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#include<stdio.h>
#include<algorithm>
#include<math.h>
#include<string.h>

using namespace std;

const int MAXN = 225;
int L[MAXN*MAXN], R[MAXN*MAXN], U[MAXN*MAXN], D[MAXN*MAXN];
int S[MAXN];
int Col[MAXN*MAXN];
int limit;

void Remove(int x) {
	for (int i = D[x]; i != x; i = D[i]) {
		L[R[i]] = L[i];
		R[L[i]] = R[i];
	}
}
void Resume(int x) {
	for (int i = U[x]; i != x; i = U[i]) {
		L[R[i]] = R[L[i]] = i;
	}
}
int Hash() {
	int ans = 0;
	bool hash[MAXN] = {0};
	for (int c = R[0]; c != 0; c = R[c])
	if (! hash[c]) {
		hash[c] = true;
		ans ++;
		for (int i = D[c]; i != c; i = D[i])
			for (int j = R[i]; j != i; j = R[j])
				hash[Col[j]] = true;
	}
	return ans;
}

bool dfs(int depth) {
	if (depth + Hash() > limit) return false;
	if (R[0] == 0) return true;
	int i, j, c, minnum = 2000000000;
	for (i = R[0]; i != 0; i = R[i]) {
		if (S[i] < minnum) {
			minnum = S[i];
			c = i;
		}
	}
	for (i = U[c]; i != c; i = U[i]) {
		Remove(i);
		for (j = R[i]; j != i; j = R[j]) Remove(j);
		if (dfs(depth + 1)) {
			for (j = L[i]; j != i; j = L[j]) Resume(j);
			Resume(i);
			return true;
		}
		for (j = L[i]; j != i; j = L[j]) Resume(j);
		Resume(i);
	}
	return false;
}

int solve(int n, int m, int DL[][MAXN], int maxdepth) {
	if (maxdepth > n) maxdepth = n;
	for (int i = 0; i <= m; i ++) {
		L[i] = i - 1;
		R[i] = i + 1;
		U[i] = D[i] = i;
	}
	L[0] = m;
	R[m] = 0;
	int cnt = m + 1;
	memset(S, 0, sizeof (S));
	for (int i = 1; i <= n; i ++) {
		int head = cnt, tail = cnt;
		for (int c = 1; c <= m; c ++) if (DL[i][c]) {
			S[c] ++;
			Col[cnt] = c;
			U[D[c]] = cnt;
			D[cnt] = D[c];
			U[cnt] = c;
			D[c] = cnt;
			L[cnt] = tail;
			R[tail] = cnt;
			R[cnt] = head;
			L[head] = cnt;
			tail = cnt;
			cnt ++;
		}
	}
	int best = 0, worst = maxdepth;
	/*while (best <= worst) {
		limit = (worst + best) >> 1;
		if (dfs(0)) worst = limit - 1;
		else best = limit + 1;
	}*/
	limit = maxdepth;
	if(dfs(0))best = maxdepth;
	else
		best = maxdepth+1;
	return best;
}

int x[155],y[155];

int dij(int i, int j)
{
	int d1 = (x[i]-x[j])*(x[i]-x[j]);
	int d2 = (y[i]-y[j])*(y[i]-y[j]);
	return d1+d2;
}

int main()
{
	int i,j,k,l,row,col,n,m,low,up,mid,mark[MAXN][MAXN],d[55][55],T,b[3000],top;
 
	scanf("%d",&T);
	while(T--)
	{
		scanf("%d %d %d",&n,&row,&m);

		for(i=1;i<=n+row;i++)
			scanf("%d %d",&x[i],&y[i]);
 
		low = 1; up = 1000000000;

		while(low < up)
		{
			for(i=1;i<=row;i++)
				for(j=1;j<=n;j++)mark[i][j] = 0;
   
			mid = (low + up)>>1;
			for(i=1;i<=row;i++)
				for(j=1;j<=n;j++)if(dij(i+n,j) <= mid)mark[i][j] = 1;
	
			if(solve(row, n, mark, m) > m)low = mid+1; else up = mid;
		}
		mid = (low + up)>>1;
		printf("%.6lf\n",sqrt(1.0*mid));
	}
	return 0;
}

dancing links code 1-3

一、fzu 1686
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#include<stdio.h>
#include<algorithm>

using namespace std;

const int MAXN = 225;
int L[MAXN*MAXN], R[MAXN*MAXN], U[MAXN*MAXN], D[MAXN*MAXN];
int S[MAXN];
int Col[MAXN*MAXN];
int limit;

void Remove(int x) {
	for (int i = D[x]; i != x; i = D[i]) {
		L[R[i]] = L[i];
		R[L[i]] = R[i];
	}
}
void Resume(int x) {
	for (int i = U[x]; i != x; i = U[i]) {
		L[R[i]] = R[L[i]] = i;
	}
}
int Hash() {
	int ans = 0;
	bool hash[MAXN] = {0};
	for (int c = R[0]; c != 0; c = R[c])
	if (! hash[c]) {
		hash[c] = true;
		ans ++;
		for (int i = D[c]; i != c; i = D[i])
			for (int j = R[i]; j != i; j = R[j])
				hash[Col[j]] = true;
	}
	return ans;
}

bool dfs(int depth) {
	if (depth + Hash() > limit) return false;
	if (R[0] == 0) return true;
	int i, j, c, minnum = INT_MAX;
	for (i = R[0]; i != 0; i = R[i]) {
		if (S[i] < minnum) {
			minnum = S[i];
			c = i;
		}
	}
	for (i = U[c]; i != c; i = U[i]) {
		Remove(i);
		for (j = R[i]; j != i; j = R[j]) Remove(j);
		if (dfs(depth + 1)) {
			for (j = L[i]; j != i; j = L[j]) Resume(j);
			Resume(i);
			return true;
		}
		for (j = L[i]; j != i; j = L[j]) Resume(j);
		Resume(i);
	}
	return false;
}

int solve(int n, int m, int DL[][MAXN], int maxdepth) {
	if (maxdepth > n) maxdepth = n;
	for (int i = 0; i <= m; i ++) {
		L[i] = i - 1;
		R[i] = i + 1;
		U[i] = D[i] = i;
	}
	L[0] = m;
	R[m] = 0;
	int cnt = m + 1;
	memset(S, 0, sizeof (S));
	for (int i = 1; i <= n; i ++) {
		int head = cnt, tail = cnt;
		for (int c = 1; c <= m; c ++) if (DL[i][c]) {
			S[c] ++;
			Col[cnt] = c;
			U[D[c]] = cnt;
			D[cnt] = D[c];
			U[cnt] = c;
			D[c] = cnt;
			L[cnt] = tail;
			R[tail] = cnt;
			R[cnt] = head;
			L[head] = cnt;
			tail = cnt;
			cnt ++;
		}
	}
	int best = 0, worst = maxdepth;
	while (best <= worst) {
		limit = (worst + best) >> 1;
		if (dfs(0)) worst = limit - 1;
		else best = limit + 1;
	}
	return best;
}

int main()
{
	int i,j,k,l,row,col,n,m,n1,m1,mark[MAXN][MAXN],a[33][33],id[33][33];
 
	while(scanf("%d %d",&n,&m) != EOF)
	{
		col = 0;
		for(i=1;i<=n;i++)
			for(j=1;j<=m;j++)
			{
				scanf("%d",&a[i][j]);
				id[i][j] = -1;
				if(a[i][j] == 1) { col++; id[i][j] = col; }
			}
		scanf("%d %d",&n1,&m1);

		row = 0;
		for(i=1;i<=n-n1+1;i++)
			for(j=1;j<=m-m1+1;j++)
			{
				row++;
				for(k=1;k<=col;k++)mark[row][k] = 0;
 
				for(k=i;k<i+n1;k++)
					for(l=j;l<j+m1;l++)
					if(id[k][l] > 0)
						mark[row][id[k][l]] = 1;
			}
 
		printf("%d\n",solve(row, col, mark, row));
	}
	return 0;
}

二、zju 3209
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#include<stdio.h>
#include<algorithm>
#include<math.h>
#include<string.h>

using namespace std;

const int MAXN = 1005;
int L[MAXN*MAXN], R[MAXN*MAXN], U[MAXN*MAXN], D[MAXN*MAXN];
int S[MAXN];
int Col[MAXN*MAXN], Row[MAXN*MAXN],ans,limit,up;


void Remove(int c) {
	L[R[c]] = L[c];
	R[L[c]] = R[c];
	for (int i = D[c]; i != c; i = D[i])
	for (int j = R[i]; j != i; j = R[j]) {
		U[D[j]] = U[j];
		D[U[j]] = D[j];
		-- S[Col[j]];
	}
}
void Resume(int c) {
	for (int i = U[c]; i != c; i = U[i])
	for (int j = L[i]; j != i; j = L[j]) {
		U[D[j]] = j;
		D[U[j]] = j;
		++ S[Col[j]];
	}
	L[R[c]] = c;
	R[L[c]] = c;
}

bool dfs(int depth) {
	if (depth >= ans) return true;
 
	if(R[0] == 0) { if(depth < ans)ans = depth;  return true; }
 
	int i, j, c, minnum = 2000000000, flag = 0;
	for (i = R[0]; i != 0; i = R[i]) {
		if (S[i] < minnum) {
			minnum = S[i];
			c = i;
		}
	}
	Remove(c);
	for (i = U[c]; i != c; i = U[i]) {
		//如果需要的话,在这里记录一组解(Ans[depth] = Row[i])
		for (j = R[i]; j != i; j = R[j]) Remove(Col[j]);
		if (dfs(depth + 1)) flag = 1; //return true;
		for (j = L[i]; j != i; j = L[j]) Resume(Col[j]);
	}
	Resume(c);
	return flag;//false;
}
int solve(int n, int m, int DL[][MAXN]) {
	for (int i = 0; i <= m; i ++) {
		L[i] = i - 1;
		R[i] = i + 1;
		U[i] = D[i] = i;
	}
	L[0] = m;
	R[m] = 0;
	int cnt = m + 1;
	memset(S, 0, sizeof (S));
	for (int i = 1; i <= n; i ++) {
		int head = cnt, tail = cnt;
		for (int c = 1; c <= m; c ++) if (DL[i][c]) {
			S[c] ++;
			Row[cnt] = i;
			Col[cnt] = c;
			U[D[c]] = cnt;
			D[cnt] = D[c];
			U[cnt] = c;
			D[c] = cnt;
			L[cnt] = tail;
			R[tail] = cnt;
			R[cnt] = head;
			L[head] = cnt;
			tail = cnt;
			cnt ++;
		}
	}
	if (dfs(0)) return true;
	return false;
}

int mark[MAXN][MAXN];

int main()
{
	int i,j,k,l,n,m,T,row,col,x1,x2,y1,y2,id[33][33],low;
	scanf("%d",&T);
	while(T--)
	{
		scanf("%d %d %d",&n,&m,&row);
		col = 0;
		for(i=1;i<=n;i++)
			for(j=1;j<=m;j++)
			{
				col++; id[i][j] = col;
			}
 
		for(i=1;i<=row;i++)
			for(j=1;j<=col;j++)mark[i][j] = 0;

		for(i=1;i<=row;i++)
		{
			scanf("%d %d %d %d",&x1,&y1,&x2,&y2);
			x1++; y1++;
			for(k=x1;k<=x2;k++)
				for(l=y1;l<=y2;l++)
				mark[i][id[k][l]] = 1;
		}

		ans = 1000000000;
		if(!solve(row, col, mark))ans = -1;

		printf("%d\n",ans);
	}
	return 0;
}

三、hdu 3529
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#include<stdio.h>
#include<algorithm>

using namespace std;

const int MAXN = 225;
int L[MAXN*MAXN], R[MAXN*MAXN], U[MAXN*MAXN], D[MAXN*MAXN];
int S[MAXN];
int Col[MAXN*MAXN];
int limit;

void Remove(int x) {
	for (int i = D[x]; i != x; i = D[i]) {
		L[R[i]] = L[i];
		R[L[i]] = R[i];
	}
}
void Resume(int x) {
	for (int i = U[x]; i != x; i = U[i]) {
		L[R[i]] = R[L[i]] = i;
	}
}
int Hash() {
	int ans = 0;
	bool hash[MAXN] = {0};
	for (int c = R[0]; c != 0; c = R[c])
	if (! hash[c]) {
		hash[c] = true;
		ans ++;
		for (int i = D[c]; i != c; i = D[i])
		for (int j = R[i]; j != i; j = R[j])
		hash[Col[j]] = true;
	}
	return ans;
}

bool dfs(int depth) {
	if (depth + Hash() > limit) return false;
	if (R[0] == 0) return true;
	int i, j, c, minnum = 2000000000;
	for (i = R[0]; i != 0; i = R[i]) {
		if (S[i] < minnum) {
			minnum = S[i];
			c = i;
		}
	}
	for (i = U[c]; i != c; i = U[i]) {
		Remove(i);
		for (j = R[i]; j != i; j = R[j]) Remove(j);
		if (dfs(depth + 1)) {
			for (j = L[i]; j != i; j = L[j]) Resume(j);
			Resume(i);
			return true;
		}
		for (j = L[i]; j != i; j = L[j]) Resume(j);
		Resume(i);
	}
	return false;
}

int solve(int n, int m, int DL[][MAXN], int maxdepth) {
	if (maxdepth > n) maxdepth = n;
	for (int i = 0; i <= m; i ++) {
			L[i] = i - 1;
			R[i] = i + 1;
			U[i] = D[i] = i;
		}
		L[0] = m;
		R[m] = 0;
		int cnt = m + 1;
		memset(S, 0, sizeof (S));
		for (int i = 1; i <= n; i ++) {
			int head = cnt, tail = cnt;
			for (int c = 1; c <= m; c ++) if (DL[i][c]) {
				S[c] ++;
				Col[cnt] = c;
				U[D[c]] = cnt;
				D[cnt] = D[c];
				U[cnt] = c;
				D[c] = cnt;
				L[cnt] = tail;
				R[tail] = cnt;
				R[cnt] = head;
				L[head] = cnt;
				tail = cnt;
				cnt ++;
			}
		}
		int best = 0, worst = maxdepth;
		while (best <= worst) {
		limit = (worst + best) >> 1;
		if (dfs(0)) worst = limit - 1;
		else best = limit + 1;
	}
	return best;
}

int n,m,M[MAXN][MAXN];

int main()
{
	int i,j,k,l,row,col,idr[33][33],idc[33][33];
   
	char ch[33][33];
	while(scanf("%d %d",&n,&m) != EOF)
	{
		for(i=1;i<=n;i++) scanf("%s",ch[i]+1);
	   
		row = col = 0;
	   
		for(i=1;i<=n;i++)
			for(j=1;j<=m;j++)
			if(ch[i][j] == '.') idr[i][j] = ++row;
			else
			if(ch[i][j] == '#') idc[i][j] = ++col;
		   
		for(i=0;i<=row;i++) for(j=0;j<=col;j++) M[i][j] = 0;
	   
		for(i=1;i<=n;i++)
			for(j=1;j<=m;j++)
			if(ch[i][j] == '.')
			{
				k = i-1; l = j; while(k > 0 && ch[k][l] == '.') k--;
				if(k > 0 && ch[k][l] == '#') M[idr[i][j]][idc[k][l]] = 1;
			   
				k = i+1; l = j; while(k <= n && ch[k][l] == '.') k++;
				if(k <= n && ch[k][l] == '#') M[idr[i][j]][idc[k][l]] = 1;
			   
				k = i; l = j-1; while(l > 0 && ch[k][l] == '.') l--;
				if(l > 0 && ch[k][l] == '#') M[idr[i][j]][idc[k][l]] = 1;
			   
				k = i; l = j+1; while(l <= m && ch[k][l] == '.') l++;
				if(l <= m && ch[k][l] == '#') M[idr[i][j]][idc[k][l]] = 1;
			}
		   
		int ans = solve(row, col, M, col);
		printf("%d\n",ans);
	}
	return 0;  
}