- Maximal Square
Given a 2D binary matrix filled with 0's and 1's, find the largest square containing only 1's and return its area.
Example:
Input:
1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0
Output: 4
解 动态规划，设(dp[i][j])表示下标为(i, j)的左上角区域的最大正方形面积，当(mathrm{matrix}[i][j] eq '0')时：
[dp[i][j] = min{dp[i-1][j], dp[i][j-1], dp[i-1][j-1]}
]
class Solution {
public:
int maximalSquare(vector<vector<char>>& matrix) {
if(matrix.size() == 0)return 0;
int m = matrix.size(), n = matrix[0].size();
int *dp = new int[n+1];
memset(dp, 0, (n+1)*sizeof(int));
int ans = 0, prev = 0;
for(int i = 1; i <= m; ++i){
prev = dp[0];
for(int j = 1; j <= n; ++j){
int tmp = dp[j];
if(matrix[i-1][j-1] == '1'){
dp[j]=min(dp[j], min(prev, dp[j-1]))+1;
ans = max(ans, dp[j]);
}else{
dp[j] = 0;
}
prev = tmp;
}
}
return ans*ans;
}
};