[Leetcode] #221 Maximal Square (DP)

DIscription:

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

For example, given the following matrix:

1 0 1 0 01 0 1 1 11 1 1 1 11 0 0 1 0

Return 4.

Solution:

int maximalSquare(vector<vector<char>>& matrix) {if (matrix.empty())return 0;int rows = matrix.size(), cols = matrix[0].size();vector<vector<int>> len(rows, vector<int>(cols, 0));int maxlen = 0;for (int i = 0; i < rows; i++){len[i][0] = matrix[i][0] - '0';if (len[i][0] == 1)maxlen = 1;}for (int i = 0; i < cols; i++){len[0][i] = matrix[0][i] - '0';if (len[0][i] == 1)maxlen = 1;}for (int i = 1; i < rows; i++){for (int j = 1; j < cols; j++){if (matrix[i][j] == '0')len[i][j] = 0;else{len[i][j] = min(min(len[i - 1][j], len[i][j - 1]), len[i - 1][j - 1]) + 1;if (len[i][j]>maxlen)maxlen = len[i][j];}}}return maxlen*maxlen;}