135. Candy

题目：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?

代码实现如下：

class Solution {
public:
    int candy(vector<int>& ratings) {
        if (ratings.size() < 2) return ratings.size();
        int n = ratings.size();
        vector<int> num(n, 1);

        //from left to right
        for (int i = 1; i < n; i++) {
            if (ratings[i] > ratings[i-1]) {
                num[i] = num[i-1]+1;
            }
        }

        //from right to left
        for (int i = n-2; i >= 0; i--) {
            if (ratings[i] > ratings[i+1]) {
                num[i] = max(num[i], num[i+1]+1);
            }
        }

        int res = 0;

        for (int i = 0; i < n; i++) {
            res += num[i];
        }
        return res;
    }
};