neighbors就是指左边一个和右边一个, 只有比neighbor的rating高的孩子得到的糖才能更多, rating为1, 2, 2时糖数为1, 2, 1。正向扫一遍, 后一个比前一个rating高则后一个的糖数要增加, 再反向扫一遍, 同样处理。

class Solution:
    # @param ratings, a list of integer
    # @return an integer
    def candy(self, ratings):
        length = len(ratings)
        candy = [1 for i in xrange(length)]
        for i in xrange(length - 1):
            if ratings[i+1] > ratings[i] and candy[i+1] <= candy[i]:
                candy[i+1] = candy[i] + 1
        for i in reversed(xrange(1, length)):
            if ratings[i-1] > ratings[i] and candy[i-1] <= candy[i]:
                candy[i-1] = candy[i] + 1
        return sum(candy)