LeetCode84.柱状图中最大矩形

class Solution {
public:
    int largestRectangleArea(vector<int>& heights) {
        int size = heights.size();
        int n = heights.size();
        vector<int> left(size, -1);
        stack<int> st;
        st.push(0);
        //找到每个柱子左侧小于它高度的最近元素的下标
        for(int i = 1; i < size; i++){
            while(!st.empty() && heights[st.top()] >= heights[i])
                st.pop();
            if(!st.empty())
                left[i] = st.top();
            st.push(i);
        }
        vector<int> right(size, n);
        stack<int> st2;
        st2.push(n - 1);
        //找到每个柱子左侧小于它高度的最近元素的下标
        for(int i = n - 2; i >= 0; i--){
            while(!st2.empty() && heights[st2.top()] >= heights[i])
                st2.pop();
            if(!st2.empty())
                right[i] = st2.top();
            st2.push(i);
        }
        int res = 0;
        for(int i = 0; i < size; i++){
            res = max(res, heights[i] * (right[i] - left[i] - 1));
        }
        return res;
    }
};