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221. 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.
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.
本题一定要注意，做动态规划方法的时候，dp里面的值不能够存储面积属性，之能存储边长。因为面积属性到时候还需要开平方根。代码如下：
<style>p.p1 { margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px "Helvetica Neue"; color: #454545 }</style>public class Solution {
public int maximalSquare(char[][] matrix) {
if(matrix==null||matrix.length==0||matrix[0].length==0) return 0;
int m = matrix.length;
int n = matrix[0].length;
int max = 0;
int[][] dp = new int[m][n];
for(int i=0;i<m;i++){
if(matrix[i][0]==‘1‘) dp[i][0] = 1;
max = Math.max(dp[i][0],max);
}
for(int i=0;i<n;i++){
if(matrix[0][i]==‘1‘) dp[0][i] = 1;
max = Math.max(dp[0][i],max);
}
for(int i=1;i<m;i++){
for(int j=1;j<n;j++){
if(matrix[i][j]==‘1‘){
if(dp[i-1][j-1]!=0&&dp[i-1][j]!=0&&dp[i][j-1]!=0){
dp[i][j] = Math.min(dp[i-1][j-1],Math.min(dp[i][j-1],dp[i-1][j]))+1;
max = Math.max(max,dp[i][j]);
}else{
dp[i][j] = 1;
}
}
}
}
return max*max;
}
}
221. Maximal Square