Leetcode176: Maximal Square

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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 01 0 1 1 11 1 1 1 11 0 0 1 0

Return 4.

用动态规划的思想，令res[i][j]表示以i,j为右下角坐标的正方形的最大边长，则 res[i][j] = min(min(res[i-1][j], res[i][j-1]), res[i-1][j-1])+1

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

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