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.

class Solution {
public:
    int maximalSquare(vector<vector<char>>& matrix) {
        int rows = matrix.size();
        if (rows < 1) {
            return 0;
        }
        int cols = matrix[0].size();
        if (cols < 1) {
            return 0;
        }
        
        vector<int> dp0(cols + 1, 0);
        vector<int> dp1(cols + 1, 0);
        
        int dlen = 0;
        for (int i=1; i<=rows; i++) {
            for (int j=1; j<=cols; j++) {
                if (matrix[i-1][j-1] == '0') {
                    dp1[j] = 0;
                } else {
                    dp1[j] = min(dp1[j-1], min(dp0[j], dp0[j-1])) + 1;
                }
                dlen = max(dlen, dp1[j]);
            }
            swap(dp0, dp1);
        }
        return dlen * dlen;
    }
};

dp写起来爽，想起来不爽