LeetCode in Net

221. Maximal Square

Medium

Given an m x n binary matrix filled with 0’s and 1’s, find the largest square containing only 1’s and return its area.

Example 1:

Input: matrix = [[“1”,”0”,”1”,”0”,”0”],[“1”,”0”,”1”,”1”,”1”],[“1”,”1”,”1”,”1”,”1”],[“1”,”0”,”0”,”1”,”0”]]

Output: 4

Example 2:

Input: matrix = [[“0”,”1”],[“1”,”0”]]

Output: 1

Example 3:

Input: matrix = [[“0”]]

Output: 0

Constraints:

• m == matrix.length
• n == matrix[i].length
• 1 <= m, n <= 300
• matrix[i][j] is '0' or '1'.

Solution

public class Solution {
    public int MaximalSquare(char[][] matrix) {
        int m = matrix.Length;
        if (m == 0) {
            return 0;
        }
        int n = matrix[0].Length;
        if (n == 0) {
            return 0;
        }
        int[][] dp = new int[m + 1][];
        for (int i = 0; i <= m; i++) {
            dp[i] = new int[n + 1];
        }
        int max = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] == '1') {
                    // 1 + minimum from cell above, cell to the left, cell diagonal upper-left
                    int next = 1 + Math.Min(dp[i][j], Math.Min(dp[i + 1][j], dp[i][j + 1]));
                    // keep track of the maximum value seen
                    if (next > max) {
                        max = next;
                    }
                    dp[i + 1][j + 1] = next;
                }
            }
        }
        return max * max;
    }
}

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