Candy

LeetCode Q 135 - Candy

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

Two-pass solution, for one pass we only consider the left restriction, and for another we add the right constraint.

Code:

public int candy(int[] ratings) {

	if (ratings == null || ratings.length == 0)
		return 0;

	int[] arr = new int[ratings.length];
	Arrays.fill(arr, 1);

	for (int i = 1; i < ratings.length; i++) {
		if (ratings[i] > ratings[i - 1])
			arr[i] = arr[i - 1] + 1;
	}

	int sum = arr[ratings.length - 1];
	for (int i = ratings.length - 2; i >= 0; i--) {
		if (ratings[i] > ratings[i + 1])
			arr[i] = Math.max(arr[i], arr[i + 1] + 1);
		sum += arr[i];
	}

	return sum;
}