[LeetCode] 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.

DP: If matrix[i][j] == 1, D[i][j] = min(D[i][j-1], D[i-1][j], D[i-1][j-1]) + 1;

class Solution {
public:
    int maximalSquare(vector<vector<char>>& matrix) {
        int m = matrix.size();
        if(0 == m) return 0;
        int n = matrix[0].size();
        
        vector<vector<int>> D(m, vector<int>(n, 0));
        int res = 0;
        
        for(int i=0;i<m;i++)
        {
            D[i][0] = matrix[i][0] - '0';
            if(D[i][0] == 1) res = 1;
        }
        
        for(int i=0;i<n;i++)
        {
            D[0][i] = matrix[0][i] - '0';
            if(D[0][i] == 1) res = 1;
        }
        
        for(int i=1;i<m;i++)
        {
            for(int j=1;j<n;j++)
            {
                if(matrix[i][j]-'0' == 1)
                {
                    D[i][j] = min(D[i-1][j-1], 
                        min(D[i-1][j], D[i][j-1])) + 1;
                    res = max(D[i][j], res);
                }
            }
        }
        return res*res;
    }
};