Leetcode84. 柱状图中最大的矩形 -hot100

题目：

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代码(首刷看解析 2024年3月9日）：

class Solution {
public:
    int largestRectangleArea(vector& heights) {
        int result = 0;
        vector st;//存放柱子下标
        heights.insert(heights.begin(), 0);//哨兵
        heights.push_back(0);//哨兵
        for (int i = 0; i < heights.size(); ++i) {
            while (!st.empty() && heights[i] < heights[st.back()]) {
                int height = st.back();
                st.pop_back();
                int left = st.back() + 1;
                int right = i - 1;
                result = max(result, (right - left + 1) * heights[height]);
            }
            st.emplace_back(i);
        }
        return result;
    }
};

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代码（二刷看解析 2024年3月17日 双指针）

class Solution {
public:
    int largestRectangleArea(vector& heights) {
        int size = heights.size();
        vector minLeftIndex(size);
        vector minRightIndex(size);

        minLeftIndex[0] = -1;
        for (int i = 1; i < size; ++i)
        {
            int t = i - 1;
            while (t >= 0 && heights[t] >= heights[i]) t = minLeftIndex[t];
            minLeftIndex[i] = t;
        }

        minRightIndex[size - 1] = size;
        for (int i = size - 2; i >= 0; --i)
        {
            int t = i + 1;
            while (t < size && heights[t] >= heights[i]) t = minRightIndex[t];
            minRightIndex[i] = t;
        }

        int result = 0;
        for (int i = 0; i < size; ++i)
        {
            int sum = heights[i] * (minRightIndex[i] - minLeftIndex[i] - 1);
            result = max(sum, result);
        }
        return result;
    }
};