Maximal Square 解答

Question

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.

Solution

2-D array. The changing condition is:

t[i][j] = min(t[i][j-1], t[i-1][j], t[i-1][j-1]) + 1.

 public class Solution {
     public int maximalSquare(char[][] matrix) {
         if (matrix == null || matrix.length < 1)
             return 0;
         int row = matrix.length, column = matrix[0].length, max = 0;
         int[][] dp = new int[row][column];
         // Top Row
         for (int i = 0; i < column; i++) {
             if (matrix[0][i] == '0')
                 dp[0][i] = 0;
             else
                 dp[0][i] = 1;
         }
         // Left Column
         for (int i = 0; i < row; i++) {
             if (matrix[i][0] == '0')
                 dp[i][0] = 0;
             else
                 dp[i][0] = 1;
         }
         // Inside Filling
         for (int i = 1; i < row; i++) {
             for (int j = 1; j < column; j++) {
                 if (matrix[i][j] == '0') {
                     dp[i][j] = 0;
                 } else {
                     int tmp = Math.min(dp[i][j - 1], dp[i - 1][j]);
                     dp[i][j] = Math.min(tmp, dp[i - 1][j - 1]) + 1;
                 }
             }
         }
         for (int i = 0; i < row; i++) {
             for (int j = 0; j < column; j++)
                 max = Math.max(max, dp[i][j]);
         }
         return max * max;
     }
 }