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 0
1 0 1 1 1
1 1 1 1 1
1 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;
else
dp[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;
}
};