Maximal Square

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