LeetCode: Candy 解题报告

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?

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SOLUTION:

使用一个数组记录每一个小孩应得的糖果的数目

1.我们可以从左往右扫描，如果遇到上升区间，就给小孩比左边多一个糖，否则就给1个糖果。

2.我们可以从右往左扫描，如果遇到上升区间，就给小孩比右边多一个糖，否则就给1个糖果。

   同时，应该与1步算出的值取一个大值（因为有可能要给小孩更多糖果才可以满足题设）。

public class Solution {
    public int candy(int[] ratings) {
        if (ratings == null || ratings.length == 0) {
            return 0;
        }
        
        
        int len = ratings.length;
        int[] num = new int[len];
        
        // go from left to right;
        for (int i = 0; i < len; i++) {
            if (i > 0 && ratings[i] > ratings[i - 1]) {
                num[i] = num[i - 1] + 1;
            } else {
                num[i] = 1;
            }
        }
        
        // go from right to left;
        int sum = 0;
        for (int i = len - 1; i >= 0; i--) {
            if (i < len - 1 && ratings[i] > ratings[i + 1]) {
                num[i] = Math.max(num[i], num[i + 1] + 1);
            }
            sum += num[i];
        }
        
        return sum;
    }
}

CODE:

https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/dp/Candy.java