【面试题 & LeetCode 221】Maximal Square

题目描述

Given a 2D binary matrix filled with 0’s and 1’s, find the largest square containing only 1’s and return its area.

Example:

Input: 

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

Output: 4

思路

dp[i][j]表示以i,j位置为右下角顶点的正方形的最长的边。

代码

class Solution {
public:
    int maximalSquare(vector<vector<char>>& matrix) {
        if (matrix.empty()) return 0;
        int n = matrix.size();
        int m = matrix[0].size();
        vector<vector<int> > dp(n, vector<int>(m, 0));
    
        int max_ = 0;
        for (int i=0; i<n; ++i) {
            for (int j=0; j<m; ++j) {
                if (matrix[i][j] == '0') continue;
                if (i == 0 || j == 0) {
                    dp[i][j] = 1;
                }else {
                    dp[i][j] = min(dp[i-1][j-1], min(dp[i-1][j], dp[i][j-1])) + 1;
                }
                max_ = max(max_, dp[i][j]);
            }
        }
        
        return max_*max_;
    }
};