Leetcode 135 Candy

There are N children standing in a line. Each child is assigned a rating value.

You are giving candies to these children subjected to the following requirements:
Each child must have at least one candy.
Children with a higher rating get more candies than their neighbors.

What is the minimum candies you must give?
分糖果，每个人至少一个，得分较左右高的人要比左右的人分的多。
先是想了DP，后来发现不需要，每个人初始分一个，然后找到单调上升和单调下降的区间，区间转折点取最大值。

程序实现的时候是正一遍，反一遍来的，实现起来比较方便。

class Solution {
public:
int candy(vector<int>& ratings) {
vector<int> dp(ratings.size(), 1);
int res = 0;
for(int i = 1; i < ratings.size();i++) if(ratings[i]>ratings[i-1]) dp[i] = dp[i-1] + 1;
for(int i = ratings.size()-2;i >= 0 ;i--)
{
if(ratings[i] > ratings[i+1]) dp[i] = max(dp[i], dp[i+1] + 1) ;
res += dp[i];
}
return res + dp[ratings.size()-1];
}
};