Day60 单调栈part03 84. 柱状图中最大的矩形

Day60 单调栈part03 84. 柱状图中最大的矩形

84. 柱状图中最大的矩形

暴力法

class Solution {
public:
    int largestRectangleArea(vector<int>& heights) {
        int sum = 0;
        for (int i = 0; i < heights.size(); i++) {
            int left = i;
            int right = i;
            for (; left >= 0; left--) {
                if (heights[left] < heights[i]) break;
            }
            for (; right < heights.size(); right++) {
                if (heights[right] < heights[i]) break;
            }
            int w = right - left - 1;
            int h = heights[i];
            sum = max(sum, w * h);
        }
        return sum;
    }
};

单调栈

class Solution {
public:
    int largestRectangleArea(vector<int>& heights) {
        int result = 0;  //记录结果
        stack<int> stk;
        heights.insert(heights.begin(),0);  //头部添加元素0
        heights.push_back(0);   //尾部添加元素0
        stk.push(0);
        for(int i = 1;i<heights.size();i++){
            if(heights[i] >= heights[stk.top()]) stk.push(i);
            else{
                while(!stk.empty()&&heights[i] < heights[stk.top()]){
                    int mid = stk.top();
                    stk.pop();
                    if(!stk.empty()){
                        int height = heights[mid];
                        int width = i - stk.top()-1;
                        result = max(result,height*width);
                    }
                }
                stk.push(i);
            }
        }
        return result;
    }
};