October 27, 2019

221. Maximal Square

Range Sum Query 2D - Immutable
Largest Rectangle in Histogram

Sol 1. Brute Force

枚举左上角，对每一个左上角，

Sol 2. Dynamic Programming

Time = O(n^2), space = O(n^2)

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