动态规划例子：Maximal Square

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.

 public class Solution {
     public int maximalSquare(char[][] matrix) {
         int rows = matrix.length;
         if(rows == 0) return 0;
         int cols = matrix[0].length;
         if(cols == 0) return 0;
         Node[][] sta = new Node[rows][cols];
         for(int i=0; i<rows; i++){
             for(int j=0; j<cols; j++){
                 sta[i][j] = new Node();
             }
         }

         int res = 0;

         if(matrix[0][0] == '1'){
             sta[0][0].left = 1;
             sta[0][0].up = 1;
             sta[0][0].maxSize = 1;
             res = 1;
         }
         //求第一行
         for(int i=1; i<cols; i++){
             if(matrix[0][i] == '1'){
                 sta[0][i].left = sta[0][i-1].left+1;
                 sta[0][i].maxSize = 1;
                 res = 1;
             }
         }
         //求第一列
         for(int j=1;j<rows;j++){
             if(matrix[j][0] == '1'){
                 sta[j][0].up = sta[j-1][0].up + 1;
                 sta[j][0].maxSize = 1;
                 res = 1;
             }
         }
         //动态求其他
         for(int i=1; i<rows; i++){
             for(int j=1; j<cols; j++){
                 if(matrix[i][j] == '1'){
                     sta[i][j].left = sta[i-1][j].left + 1;
                     sta[i][j].up = sta[i][j-1].up + 1;
                     sta[i][j].maxSize = 1;
                     if(matrix[i-1][j-1] == '1'){
                         sta[i][j].maxSize = Math.min(sta[i][j].left, sta[i][j].up);
                         sta[i][j].maxSize = Math.min(sta[i][j].maxSize, sta[i-1][j-1].maxSize+1);
                     }

                 }
                 res = Math.max(sta[i][j].maxSize, res);
             }
         }

         return res*res;

     }

     class Node{
         int left;
         int up;
         int maxSize;
     }

 }