(Java) LeetCode 135. Candy —— 分发糖果

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.

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不知道如何分析这个题，很自然的思路就是先假设一个结果数组存着每个孩子要拿的糖数，初始都为1。那么先从前往后遍历ratings数组，逐个比较每一项和其前面的“邻居”。如果遍历到的孩子评分比前面高，那么他的糖数就设置为前邻居糖数+1。遍历完之后还要反着再看一遍后邻居，如果比后邻居评分高，且糖数还不如后邻居多，那么就要设置成后邻居糖数+1。本质上就是先遍历一次，分别保证评分满足和左边的邻居比，之后再遍历一次，保证评分满足和右边的邻居比。最后把每个人手里糖数加起来就是结果。

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Java

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