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) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
        	return 0;
        }
        int max = 0;
        int[] height = new int[matrix[0].length];
        for (int i = 0; i < matrix.length; i++) {
			for (int j = 0; j < matrix[0].length; j++) {
				height[j] = matrix[i][j] == '0' ? 0 : height[j] + 1;
			}
			max = Math.max(help(height), max);
		}
        return max;
    }

	private int help(int[] height) {
		// TODO Auto-generated method stub
		if (height == null || height.length == 0) {
			return 0;
		}
		int max = 0;
		Stack<Integer> stack = new Stack<>();
		for (int i = 0; i < height.length; i++) {
			while (!stack.isEmpty() && height[i] <= height[stack.peek()]) {
				int j = stack.pop();
				int k = stack.isEmpty() ? -1 : stack.peek();
				int cur = (i - k - 1) * height[j];
				max = Math.max(max, cur);
			}
			stack.push(i);
		}
		while (!stack.isEmpty()) {
			int j = stack.pop();
			int k = stack.isEmpty() ? -1 : stack.peek();
			int cur = (height.length - k - 1) * height[j];
			max = Math.max(max, cur);
		}
		return max;
	}
}