LeetCode: 221. Maximal Square
阿新 • • 發佈:2018-12-15
題目描述
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
解題思路 —— 動態規劃
利用動態規劃,將 (i, j)
問題轉換為 (i-1, j)
,(i, j-1)
和 (i-1, j-1)
三個子問題。
AC 程式碼
class Solution { public: int maximalSquare(vector<vector<char>>& matrix) { int ans = 0; for(int i = 1; i < matrix.size(); ++i) { for(int j = 1; j < matrix[i].size(); ++j) { if(matrix[i][j] == '1') { matrix[i][j] = min(min(matrix[i][j-1], matrix[i-1][j]), matrix[i-1][j-1])+1; } } } for(int i = 0; i < matrix.size(); ++i) { for(int j = 0; j < matrix[i].size(); ++j) { ans = max(ans, matrix[i][j]-'0'); } } return ans*ans; } };