usaco 3.3 Home on the Range

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题目连接：http://ace.delos.com/usacoprob2?a=pBa6fEYMjoI&S=range

题目大意：给一个n*n的矩阵，只包含01，统计边长为k的正方形，且正方形内所有元素都为1 的个数。并按边长递增顺序输出。

思路：简单dp。状态方程：f[i][j]=min(min(f[i-1][j-1],f[i-1][j]),f[i][j-1])+1; f[i][j],表示右下角坐标为i,j的最大正方形的边长。

代码：

/*ID: czq1992LANG: C++TASK: range*/#include <iostream>#include <cstdio>#include <cstring>using namespace std;int map[255][255],ans[255],f[255][255];int n;int main(){    int i,j,k;    char c;    freopen("range.in","r",stdin);    freopen("range.out","w",stdout);    cin>>n;    getchar();    for(i=1; i<=n; i++)    {        for(j=1; j<=n; j++)        {            //cin>>c;            c=getchar();            map[i][j]=c-'0';        }        getchar();    }    for(i=1; i<=n; i++)        for(j=1; j<=n; j++)        {            if(map[i][j])            {                f[i][j]=min(min(f[i-1][j-1],f[i-1][j]),f[i][j-1])+1;            }        }    for(i=1; i<=n; i++)        for(j=1; j<=n; j++)            if(f[i][j])            {                for(k=2;k<=f[i][j];k++) ans[k]++;            }    for(i=2; i<=250; i++)        if(ans[i]) cout<<i<<" "<<ans[i]<<endl;    return 0;}/*Compiling...Compile: OKExecuting...   Test 1: TEST OK [0.000 secs, 3740 KB]   Test 2: TEST OK [0.000 secs, 3740 KB]   Test 3: TEST OK [0.000 secs, 3740 KB]   Test 4: TEST OK [0.000 secs, 3740 KB]   Test 5: TEST OK [0.000 secs, 3740 KB]   Test 6: TEST OK [0.011 secs, 3740 KB]   Test 7: TEST OK [0.011 secs, 3740 KB]All tests OK.*/