LeetCode 1277. 统计全为 1 的正方形子矩阵

原题目：https://leetcode-cn.com/problems/count-square-submatrices-with-all-ones/

思路：

如果边长是n，那么他可以构成n个正方形。见下图

代码：

class Solution {
public:
    int countSquares(vector<vector<int>>& matrix) {
        if(matrix.size() == 0 || matrix[0].size()==0) return 0;
        int row=matrix.size(),col = matrix[0].size();
        int sum = 0;
        vector<vector<int>>dp(row,vector<int>(col));
        for(int i=0;i<row;i++)
            for(int j = 0;j<col;j++)
                if(matrix[i][j] ==1){
                    if(i==0 || j == 0)
                        dp[i][j] =1;
                    else
                        dp[i][j] = min(min(dp[i-1][j],dp[i-1][j-1]),dp[i][j-1]) + 1;
                   sum += dp[i][j];
                }
        return sum;
    }
};