Maximal Square

Desicription

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:

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Input:
1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0
Output: 4

Solution

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class Solution {
public:
int maximalSquare(vector<vector<char>>& matrix) {
if(matrix.empty())
return 0;
int row_size = matrix.size();
int col_size = matrix[0].size();
vector<int> left(col_size, 0);
vector<int> right(col_size, col_size);
vector<int> height(col_size, 0);
int res = 0;
for(int i = 0; i < row_size; i++){
int cur_left = 0;
int cur_right = col_size;
for(int j = 0; j < col_size; j++){
if(matrix[i][j] == '1')
height[j]++;
else
height[j] = 0;
}
for(int j = 0; j < col_size; j++){
if(matrix[i][j] == '1')
left[j] = max(left[j], cur_left);
else
left[j] = 0, cur_left = j + 1;
}
for(int j = col_size - 1; j >= 0; j--){
if(matrix[i][j] == '1')
right[j] = min(right[j], cur_right);
else
right[j] = col_size, cur_right = j;
}
for(int j = 0; j < col_size; j++) {
res = max(res, (min((right[j] - left[j]), height[j]) * min((right[j] - left[j]), height[j])));
}
}
return res;
}
};