Candy
Created: March 9, 2020 by [lek-tin]
Last updated: March 9, 2020
There are N children standing in a line. Each child is assigned a rating value.
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.
- What is the minimum candies you must give?
Example 1
Input: [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: [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.
Solution (greedy bi-directional scans)
Time: O(N)
Space: O(N)
class Solution:
def candy(self, ratings: List[int]) -> int:
if not ratings or len(ratings)==0:
return 0
total = 0
leftToRight = [1] * len(ratings)
rightToLeft = [1] * len(ratings)
for i in range(1, len(ratings)):
if ratings[i] > ratings[i-1]:
leftToRight[i] = leftToRight[i-1]+1
for i in range(len(ratings)-2, -1, -1):
if ratings[i] > ratings[i+1]:
rightToLeft[i] = rightToLeft[i+1]+1
for i in range(len(ratings)):
total += max(leftToRight[i], rightToLeft[i])
return total