135. Candy (Hard)

https://leetcode.com/problems/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.

Solutions

class Solution {
    public int candy(int[] ratings) {
        int len = ratings.length;
        int[] candy = new int[len];

        // Each kid at least is allocated 1 candy
        for (int i = 0; i < len; i++) {
            candy[i] = 1;
        }

        // traverse from left to right, for each ascending rating pair, allocate one
        // more candy to the right kid who carries larger value.
        for (int i = 1; i < len; i++) {
            if (ratings[i] > ratings[i - 1]) {
                candy[i] = candy[i - 1] + 1;
            }
        }

        // similar with above operations, scan from right to left
        for (int i = len - 2; i >= 0; i--) {
            if ((ratings[i] > ratings[i + 1]) && (candy[i] <= candy[i + 1])) {
                candy[i] = candy[i + 1] + 1;
            }
        }

        int num = 0;
        for (int i = 0; i < len; i++) {
            num += candy[i];
        }

        return num;
    }
}

Incorrect Solutions

References

https://www.programcreek.com/2014/03/leetcode-candy-java/

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