Candy [Leetcode]

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?

Solution: scan twice: find out the inversion and correct the number of candies for the corresponding child.

class Solution {
public:
    int candy(vector<int> &ratings) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int n = ratings.size();
        vector<int> res(n, 1);
        if(n==0) return 0;
        for(int i=1; i<n; ++i){
             if(ratings[i]>ratings[i-1])
                res[i] = res[i-1]+1;
        }
        for(int i=n-2; i>=0; --i){
            if(ratings[i]>ratings[i+1] && res[i]<=res[i+1])
                res[i] = res[i+1]+1;
        }
        int sum = 0;
        for(int i=0; i<n; ++i)
            sum+=res[i];
        return sum;
    }
};