leetcode84 柱状图
O(n^2) time 应用heights[r]<=heights[r+1]剪枝;
class Solution {
public:
int largestRectangleArea(vector<int>& heights) {
int n=heights.size();
int res=0;
for(int r=0;r<n;r++){
if(r<n-1 && heights[r]<=heights[r+1]) continue;
int h=heights[r];
for(int l=r;l>=0;l--){
if(heights[l]<h) h=heights[l];
int cur_s=(r-l+1)*h;
if(res<cur_s) res=cur_s;
}
}
return res;
}
};