#221 Maximal Square

Description

Given an m x n binary matrix filled with 0’s and 1’s, find the largest square containing only 1’s and return its area.

Examples

Example 1:

Example 2:

Example 3:

Constraints:

思路

dp，存的是以i，j为右下角的最大square边长，要注意的就是给出的是char数组，不能直接用

代码

class Solution {
    public int maximalSquare(char[][] matrix) {
        int max = 0;
        int[][] nums = new int[matrix.length][matrix[0].length];
        for (int i = 0; i < matrix.length; i++) {
            nums[i][0] = matrix[i][0] == '1'? 1: 0;
            max = Math.max(max, nums[i][0]);
        }
        for (int i = 0; i < matrix[0].length; i++) {
            nums[0][i] = matrix[0][i] == '1'? 1: 0;
            max = Math.max(max, nums[0][i]);
        }
        
        
        for (int i = 1; i < matrix.length; i++) {
            for (int j = 1; j < matrix[i].length; j++) {
                if (matrix[i][j] == '1') {
                    nums[i][j] = Math.min(Math.min(nums[i - 1][j], nums[i][j - 1]), nums[i - 1][j - 1]) + 1;
                    max = Math.max(max, nums[i][j]);
                }
            }
        }
        
        return max * max;
    }
}