0135-candy.py

class Solution:
    def candy(self, ratings: List[int]) -> int:
        n = len(ratings)
        candies = [1]*n
        #first pass guarantees left to right order is correct
        for i in range(1, n):
            if ratings[i] > ratings[i-1]:
                candies[i] = candies[i-1] + 1
        #second pass guarantees right to left order is correct
        ans = candies[-1]
        for i in range(n-2, -1, -1):
            if ratings[i] > ratings[i+1] and candies[i] <= candies[i+1]:
                candies[i] = candies[i+1] + 1
            ans += candies[i]
        return ans