84. Largest Rectangle in Histogram

Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram.

Above is a histogram where width of each bar is 1, given height = [2,1,5,6,2,3].

The largest rectangle is shown in the shaded area, which has area = 10 unit.

Example:

Input: [2,1,5,6,2,3]
Output: 10

//----------------------------------------------错误代码----------------------------------------------------》》》》》》》》》》》》》》》
class Solution {
public:
    int largestRectangleArea(vector<int>& heights) {
        int i=0;
        const int  n=heights.size()-1;
        int a[n];
        int max;
        while(i<n){
            int temp=i;
            while(heights[i]<=heights[i+1]){
           
                a[temp]+=heights[temp];
                i++;
                
            }
            i++;
            max=max>a[temp]?max:a[temp];
        }
        return max;
        

        
    }
};

class Solution {
public:
    int largestRectangleArea(vector<int>& heights) {
        int curr_processed_num {NULL};
        int largest {0}, curr_area;
        int size = heights.size();
        int expand_left{0}, expand_right{0};
        
        for(int i = 0; i < size; ++i) {
            if(heights[i] == curr_processed_num)
                continue;
            
            expand_left = 0;
            expand_right = 0;
            
            for(int j = i+1; j < size && heights[j] >= heights[i]; ++j)
                ++expand_right;
            
            for(int j = i-1; j >= 0 && heights[j] >= heights[i]; --j)
                ++expand_left;
            
            curr_area = heights[i] * (expand_left + 1 + expand_right);
            
            if(curr_area > largest)
                largest = curr_area;
            
            curr_processed_num = heights[i];
        }
        
        return largest;
    }
};