Day015 - 135. Candy

135. Candy

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

내 풀이

class Solution:
    def candy(self, ratings: List[int]) -> int:
        n = len(ratings)
        
        # 모든 아이들에게 최소한 1개의 사탕을 주는 리스트
        candies = [1] * n
        # n이 5라면
        # [1, 2, 3, 4, 5]

        # 왼쪽에서 오른쪽으로 순회: 오른쪽 아이가 더 크면 사탕을 더 줌
        for i in range(1, n):
            if ratings[i] > ratings[i - 1]:
                candies[i] = candies[i - 1] + 1

        # 오른쪽에서 왼쪽으로 순회: 왼쪽 아이가 더 크면 사탕을 더 줌
        for i in range(n - 2, -1, -1): # 3, -1, -1
            if ratings[i] > ratings[i + 1]:
                candies[i] = max(candies[i], candies[i + 1] + 1)

        # 사탕의 총합을 계산하여 반환
        return sum(candies)

# Time Complexity : \(O(N)\)