LeetCode - 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

 

My Solution:

class Solution(object):
    def candy(self, ratings):
        """
        :type ratings: List[int]
        :rtype: int
        """
        
        n = len(ratings)
        candies = [1 for i in range(n)]

        # left to right
        for i in range(1, n):
            if ratings[i] > ratings[i-1] and candies[i] <= candies[i-1]:
                candies[i] = candies[i-1] + 1
        
        # right to left
        for i in range(n - 1 - 1, -1, -1):
            if ratings[i] > ratings[i+1] and candies[i] <= candies[i+1]:
                candies[i] = candies[i+1] + 1
        
        return sum(candies)