Maximal Square算法详解

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.

Credits:
Special thanks to @Freezen for adding this problem and creating all test cases.

题意：给定二维矩阵，包含’0’和’1’，求最大的方阵且方阵内的元素全为’1’，返回’1’的个数

题意：DP题，定义辅助空间w[rows][cols]，表示左上角方向的方阵的最大宽度则if matrix[i][j]=’0’ w[i][j]=0 else w[i][j]=1+min(w[i-1][j],w[i][j-1],w[i-1][j-1])；

    int maximalSquare(vector<vector<char>>& matrix) {        int rows = matrix.size();        if (rows == 0)return 0;        int cols = matrix[0].size();        vector<vector<int>> flag(rows, vector<int>(cols, 0));        int maxw = 0;        for (int i = 0; i <rows; i++)        {            for (int j = 0; j<cols; j++)            {                if (matrix[i][j] == '0')                {                    flag[i][j] = 0;                }                else                {                    flag[i][j] = 1;                    if (i != 0 && j != 0)                    {                        flag[i][j] += min(min(flag[i - 1][j], flag[i][j - 1]), flag[i - 1][j - 1]);                    }                }                maxw = max(flag[i][j], maxw);            }        }        return maxw*maxw;    }