Leetcode 84. 柱状图中最大的矩形

单调栈

class Solution {
public:
    int largestRectangleArea(vector<int>& heights) {
        int Len = heights.size();
        vector<int> sta, L(Len, 0), R(Len, 0);
        for (int i = 0; i < Len; ++i) {
            while (!sta.empty() && heights[sta.back()] > heights[i]) {
                int x = sta.back(); sta.pop_back();
                R[x] = i - 1;
            }
            sta.push_back(i);
        }
        while (!sta.empty()) {
            int x = sta.back(); sta.pop_back();
            R[x] = Len - 1;
        }
        for (int i = Len - 1; i >= 0; --i) {
            while (!sta.empty() && heights[sta.back()] > heights[i]) {
                int x = sta.back(); sta.pop_back();
                L[x] = i + 1;
            }
            sta.push_back(i);
        }
        while (!sta.empty()) {
            int x = sta.back(); sta.pop_back();
            L[x] = 0;
        }
        int ans = 0;
        for (int i = 0; i < Len; ++i)
            ans = max(ans, (R[i] - L[i] + 1)*heights[i]);
        return ans;

    }
};