The challenge

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.

The solution in Java code

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class Solution {
    public int candy(int[] ratings) {
        if (ratings.length==0)
            return 0;
        
        int n = ratings.length;
        int[] arr = new int[n];
        
        for (int i=0; i<n; i++) {
            arr[i] = 1;
        }
        for (int i=1; i<n; i++) {
            if (ratings[i] > ratings[i-1])
                arr[i] = 1 + arr[i-1];
        }
        for (int i=n-2; i>=0; i--){
            if (ratings[i] > ratings[i+1] && arr[i] <= arr[i+1])
                arr[i] = 1 + arr[i+1];
        }
        
        int sum=0;
        for (int i:arr) sum += i;

        return sum;
    }
}