LeetCode 135. Candy

135. Candy

Difficulty: Hard

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

Language: Java

class Solution {
    public int candy(int[] ratings) {
        if (ratings == null || ratings.length == 0) {
            return 0;
        }
        int n = ratings.length;
        int[] increaseLR = new int[n];
        for (int i = 1; i < n; i++) {
            if (ratings[i] > ratings[i - 1]) {
                increaseLR[i] = increaseLR[i - 1] + 1;
            }
        }
        
        int[] increaseRL = new int[n];
        for (int i = n - 2; i >= 0; i--) {
            if (ratings[i] > ratings[i + 1]) {
                increaseRL[i] = increaseRL[i + 1] + 1;
            }
        }
        int total = n;
        for (int i = 0; i < n; i++) {
            total += Math.max(increaseLR[i], increaseRL[i]);
        }
        return total;
    }
}