Leetcode: Candy 每个数都比相邻数大

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?

class Solution {
public:
    int candy(vector<int> &ratings) {
        std::vector<int> num(ratings.size(), 1);
        
        int inc = 2;
        for (int i = 1; i < ratings.size(); ++i) {
            if (ratings.at(i) > ratings.at(i - 1)) {
                num.at(i) = std::max(inc++, num.at(i));
            } else {
                inc = 2;
            }
        }
        inc = 2;
        for (int i = ratings.size() - 2; i >= 0; --i) {
            if (ratings.at(i) > ratings.at(i + 1)) {
                num.at(i) = std::max(inc++, num.at(i));
            } else {
                inc = 2;
            }
        }
        int res = std::accumulate(num.begin(), num.end(), 0);
        return res;
    }
};

原数组为：1 --> 2 --> 5 --> 4 --> 3 --> 2 --> 1

step2之后 num数组为：1 --> 2 --> 3 --> 1 --> 1 --> 1 --> 1

step3从右向左遍历到idx=2时 : 1 --> 2 --> （3 or 5）--> 4 --> 3 --> 2 --> 1