Maximal Square

题目
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

答案

class Solution {
    public int maximalSquare(char[][] matrix) {
        if(matrix == null || matrix.length == 0) return 0;
        int m = matrix.length, n = matrix[0].length;
        int[][] f = new int[m][n];
        
        int max = 0;
        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                if(i == 0 || j == 0) {
                    f[i][j] = (matrix[i][j] == '1') ? 1:0;
                    max = Math.max(max, f[i][j]);
                    continue;
                }
                
                int top = f[i - 1][j], left = f[i][j - 1], top_left = f[i - 1][j - 1];
                f[i][j] = (matrix[i][j] == '1') ? Math.min(top, Math.min(left, top_left)) + 1 : 0;
                max = Math.max(max, f[i][j]);
            }
        }
        return max * max;
    }
}