leecode_221 Maximal Square

Given a 2D binary matrix filled with 0's and 1's, find the largest square containing all 1's and return its area.

For example, given the following matrix:

1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0

Return 4.

使用dp解决：

构造一个新的矩阵dp，dp[i][j]表示以点(i, j)为右下角的正方形的边长；状态转移方程：

dp[i][j] = min(dp[i-1][j-1], min(dp[i-1][j], dp[i][j-1])) + 1;

class Solution {
public:
int maximalSquare(vector<vector<char>>& matrix) {
const int m=matrix.size();
if (m==0)
return 0;
const int n=matrix[0].size();
if (n==0)
return 0;
int dp[m]
;
int res=0;

for (int i=0;i<m;i++){
for (int j=0;j<n;j++){
if (matrix[i][j]=='1'){
dp[i][j]=1;
res=1;
}
else
dp[i][j]=0;
}
}

for (int i=1;i<m;i++){
for (int j=1;j<n;j++){
if (dp[i][j]==1){
dp[i][j]=min(dp[i-1][j-1], min(dp[i][j-1], dp[i-1][j]) )+1;
res=max(res,dp[i][j]);
}
}
}

return res*res;

}
};