s0135_candy

135. Candy

Hard

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

Solution

from typing import List

class Solution:
    def candy(self, ratings: List[int]) -> int:
        candies = [1] * len(ratings)
        for i in range(len(ratings) - 1):
            if ratings[i + 1] > ratings[i]:
                candies[i + 1] = candies[i] + 1
        for i in range(len(ratings) - 1, 0, -1):
            if ratings[i - 1] > ratings[i] and candies[i - 1] < candies[i] + 1:
                candies[i - 1] = candies[i] + 1
        return sum(candies)