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

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class Solution:
    def candy(self, ratings: List[int]) -> int:
        n = len(ratings)
        arr = [1] * n
        for i in range(1, n):
            if ratings[i] > ratings[i-1]:
                arr[i] = arr[i-1] + 1
        s = arr[n-1]
        for i in range(n-2, -1, -1):
            if ratings[i] > ratings[i+1]:
                arr[i] = max(arr[i], arr[i+1]+1)
            s += arr[i]
        return s