85. Maximal Rectangle

题目

 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. 

解析

• [LeetCode] Maximal Rectangle 最大矩形

// 85. Maximal Rectangle
class Solution_85 {
public:

    int largestRectangleArea(vector<int> &height) {
        int res = 0;
        stack<int> s;
        height.push_back(0);
        for (int i = 0; i < height.size(); ++i) {
            if (s.empty() || height[s.top()] <= height[i]) s.push(i);
            else {
                int tmp = s.top();
                s.pop();
                res = max(res, height[tmp] * (s.empty() ? i : (i - s.top() - 1)));
                --i;
            }
        }
        return res;
    }

    int maximalRectangle(vector<vector<char>>& matrix) {

        if (matrix.empty())
        {
            return 0;
        }
        int res = 0;

        int n = matrix.size();
        int m = matrix[0].size();

        vector<int> height(m);
        for (int i = 0; i < n;i++)
        {
            for (int j = 0; j < m;j++)
            {
                height[j] = matrix[i][j] == '0' ? 0 : (1+height[j]);
            }
            res =max(res, largestRectangleArea(height));
        }

        return res;
    }
};

题目来源

• 85. Maximal Rectangle