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?

Example

Given ratings = [1, 2], return 3.

Given ratings = [1, 1, 1], return 3.

Given ratings = [1, 2, 2], return 4. ([1,2,1]).

分析：

扫两遍。第一遍从左往右扫，保证右边大的candy数大于左边小的，否则为1.

第二遍从右往左扫，保证左边大的candy数比右边小的大，而且还必须不能低于自己当前的candy数。

public class Solution {
    /**
     * @param ratings Children's ratings
     * @return the minimum candies you must give
     */
    public int candy(int[] ratings) {
        if (ratings == null || ratings.length == 0) {
            return 0;
        }
 
        int[] candies = new int[ratings.length];
        candies[0] = 1;
     
        //from let to right, assign one more than to its right neighbor if its right 
        // neighbor has higher rating
        for (int i = 1; i < ratings.length; i++) {
            if (ratings[i] > ratings[i - 1]) {
                candies[i] = candies[i - 1] + 1;
            } else { 
                // if not ascending, assign 1
                candies[i] = 1;
            }
        }
     
        int total = candies[ratings.length - 1];
        //from right to left, assign one more candy to its left neighbor if its left neighbor
        // if its left neighbor has higher rating.
        for (int i = ratings.length - 2; i >= 0; i--) {
            int cur = 1;
            if (ratings[i] > ratings[i + 1]) {
                cur = candies[i + 1] + 1;
            }
            candies[i] = Math.max(cur, candies[i]);
            total += candies[i];
        }
        return total;
    }
}