Leetcode 85. Maximal Rectangle (Hard) (cpp)

Leetcode 85. Maximal Rectangle (Hard) (cpp)

Tag: Array, Hash Table, Stack, Dynamic Programming

Difficulty: Hard

/*

85. Maximal Rectangle (Hard)

Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing only 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 6.

*/
class Solution {
public:
	int maximalRectangle(vector<vector<char>>& matrix) {
		if (matrix.empty()) {
			return 0;
		}
		int maxRec = 0;
		vector<int> height(matrix[0].size());
		for (int i = 0; i < matrix.size(); i++) {
			for (int j = 0; j < matrix[0].size(); j++) {
				height[j] = matrix[i][j] == '0' ? 0 : height[j] + 1;
			}
			maxRec = max(maxRec, largestRectangleArea(height));
		}
		return maxRec;
	}
private:
	int largestRectangleArea(const vector<int>& heights) {
		stack<int> s;
		int maxSize = 0;
		for (int i = 0; i <= heights.size(); i++) {
			int cur = i == heights.size() ? 0 : heights[i];
			while (!s.empty() && heights[s.top()] >= cur) {
				int height = heights[s.top()];
				s.pop();
				int left = s.empty() ? 0 : s.top() + 1;
				maxSize = max(maxSize, (i - left) * height);
			}
			s.push(i);
		}
		return maxSize;
	}
};