Maximal Square

Description:

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

For example, given the following matrix:

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

Return 4.

Solution:

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