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.
For example,
Given height = [2,1,5,6,2,3],
return 10.

Solution: 1. Only calucate area when reaching local maximum value.
2. Keep a non-descending stack. O(n).

class Solution {
public:
    int largestRectangleArea(vector<int> &height) {
        int N = height.size(); 
        int res = 0;
        for(int i = 0; i < N; i++) {
            if(i < N - 1 && height[i] <= height[i+1])
                continue;
            int minHeight = INT_MAX;
            for(int j = i; j >= 0; j--) {
                minHeight = min(minHeight, height[j]);
                res = max((i-j+1)*minHeight, res);
            }
        }
        return res;
    }
};