leetcode之maximal square

题目：

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.

解答：

很明显的是一个dp，使用dp[i][j]表示以i，j为右下点的时候的最大的正方形的周长

dp[i][j] =min(min(dp[i - 1][j],dp[i][j - 1]),dp[i - 1][j - 1]);

class Solution {public:    int getVal(int i,int j,vector<vector<int>> &dp)    {if(i < 0 || i >= dp.size() || j < 0 || j >= dp[0].size())return 0;return dp[i][j];   }    int maximalSquare(vector<vector<char>>& matrix) {  int rows = matrix.size();if(!rows)return 0;int cols = matrix[0].size();if(!cols)return 0;vector<vector<int>> dp(rows,vector<int>(cols,0));int res = 0;for(int i = 0;i < rows;++i){for(int j = 0;j < cols;++j){if(matrix[i][j] == '0')dp[i][j] = 0;elsedp[i][j] = min(min(getVal(i - 1,j,dp),getVal(i, j - 1,dp)) , getVal(i - 1,j - 1,dp))  + 1;if(dp[i][j] > res)res = dp[i][j];}}      return res * res;    }};