分配糖果问题——Leetcode系列（十五）

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?

Analysis：

For one child(in the middle of three children), there are four situations of relations with his neighbors.  

1. lower, higher, highest. 
2. lower, higher, lower
3. higher,lower,higher
4. highest,higher,lower

      First, We iterate from the head to the tail, after doing this, we can calculate the candies for children who are in situation 1 and 3.

      Then, We iterate from the tail to the head, after doing this, we deal with situation 2 and 4.

      Besides, if neighbors's rating are the same, there is no need to ensure their candies are the same.

Solution:

public class Solution {
    public int candy(int[] ratings) {
        int length = ratings.length;
        if(length == 0){
            return 0;
        }else if(length == 1){
            return 1;
        }else if(length == 2){
            if(ratings[0] == ratings[1]){
                return 2;
            }else{
                return 3;
            }
        }
        int[] numbers = new int[length];
        for(int i = 0; i < length; i++){
            numbers[i] = -10000;
        }
        if(ratings[0] <= ratings[1]){
            numbers[0] = 1;
        }
        for(int i = 1; i < length - 1; i++){
            if(ratings[i] < ratings[i -1] && ratings[i] <= ratings[i + 1]){
                numbers[i] = 1;
            }else if(ratings[i] > ratings[i - 1] && ratings[i] <= ratings[i + 1]){
                numbers[i] = numbers[i -1] + 1;
            }else if(ratings[i] == ratings[i - 1] && ratings[i] <= ratings[i + 1]){
                numbers[i] = 1;
            }
        }
        if(ratings[length - 1] <= ratings[length - 2]){
            numbers[length - 1] = 1;
        }else{
            numbers[length - 1] = numbers[length -2] + 1;
        }
        for(int i = length - 2; i > 0; i--){
            if(ratings[i] > ratings[i + 1] && ratings[i] > ratings[i - 1]){
                if(numbers[i - 1] > numbers[i + 1]){
                    numbers[i] = numbers[i - 1] + 1;
                }else{
                    numbers[i] = numbers[i + 1] + 1;
                }
            }else if(ratings[i] > ratings[i + 1] && ratings[i] <= ratings[i - 1]){
                numbers[i] = numbers[i + 1] + 1;
            }else if(ratings[i] == ratings[i + 1] && ratings[i] <= ratings[i - 1]){
                numbers[i] = 1;
            }
        }
        if(ratings[0] > ratings[1]){
            numbers[0] = numbers[1] + 1;
        }
        int total = 0;
        for(int i = 0; i < length; i++){
            total += numbers[i];
        }
        return total;
    }
}

文章来源：https://oj.leetcode.com/problems/candy/