135. Candy

📋 Đề Bài

There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings.

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.

Return the minimum number of candies you need to have to distribute the candies to the children.

Example 1:

Input: ratings = [1,0,2]
Output: 5
Explanation: You can allocate to the first, second and third child with 2, 1, 2 candies respectively.

Example 2:

Input: ratings = [1,2,2]
Output: 4
Explanation: You can allocate to the first, second and third child with 1, 2, 1 candies respectively.
The third child gets 1 candy because it satisfies the above two conditions.

Constraints:

n == ratings.length
1 <= n <= 2 * 10⁴
0 <= ratings[i] <= 2 * 10⁴

💻 Lời Giải

C++ 0135-candy.cpp

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