135. Candy

Hard
Array Greedy

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 * 10^4
  • 0 <= ratings[i] <= 2 * 10^4
func candy(ratings []int) int {
	n := len(ratings)

	candies := make([]int, n)
	for i := 0; i < n; i++ {
		candies[i] = 1
	}

	for i := 1; i < n; i++ {
		if ratings[i] > ratings[i-1] {
			candies[i] = candies[i-1] + 1
		}
	}

	for i := n - 2; i >= 0; i-- {
		if ratings[i] > ratings[i+1] && candies[i] <= candies[i+1] {
			candies[i] = candies[i+1] + 1
		}
	}

	result := 0
	for i := 0; i < n; i++ {
		result += candies[i]
	}
	return result
}