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:

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1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0

Return 4.

O(mn) time O(n) space DP solution

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public class Solution {
    public int maximalSquare(char[][] matrix) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return 0;
        }
        
        int[] up = new int[matrix[0].length + 1];
        int[] cur = new int[matrix[0].length + 1];
        int size = 0;
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                if (matrix[i][j] == '1') {
                    cur[j + 1] = Math.min(Math.min(cur[j], up[j]), up[j + 1]) + 1;
                    size = Math.max(size, cur[j + 1]);
                }
            }
            up = cur;
            cur = new int[matrix[0].length + 1];
        }
        return size * size;
    }
}