[Leetcode] 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?

 

Solution:

基本思路就是进行两次扫描,一次从左往右,一次从右往左。第一次扫描的时候维护对于每一个小孩左边所需要最少的糖果数量,存入数组对应元素中,第二次扫描的时候维护右边所需的最少糖果数,并且比较将左边和右边大的糖果数量存入结果数组对应元素中。这样两遍扫描之后就可以得到每一个所需要的最最少糖果量,从而累加得出结果。方法只需要两次扫描,所以时间复杂度是O(2*n)=O(n)。空间上需要一个长度为n的数组,复杂度是O(n)。

 1 public class Solution {
 2     public int candy(int[] ratings) {
 3         if(ratings.length==0)
 4             return 0;
 5         int N=ratings.length;
 6         int[] candies=new int[N];
 7         candies[0]=1;
 8         for(int i=1;i<N;++i){
 9             if(ratings[i]>ratings[i-1]){
10                 candies[i]=candies[i-1]+1;
11             }else{
12                 candies[i]=1;
13             }
14         }
15         for(int i=N-2;i>=0;--i){
16             if(ratings[i]>ratings[i+1]&&candies[i]<=candies[i+1])
17                 candies[i]=candies[i+1]+1;
18         }
19         int result=0;
20         for(int iCandy:candies){
21             result+=iCandy;
22         }
23         return result;
24     }
25 }

 

posted @ 2014-11-24 14:56  Phoebe815  阅读(215)  评论(0编辑  收藏  举报