[LintCode] Candy 分糖果问题

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?

Have you met this question in a real interview? 

Yes

Example

Given ratings = [1, 2], return 3.

Given ratings = [1, 1, 1], return 3.

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

LeetCode上的原题，请参见我之前的博客Candy。

class Solution {
public:
    /**
     * @param ratings Children's ratings
     * @return the minimum candies you must give
     */
    int candy(vector<int>& ratings) {
        if (ratings.empty()) return 0;
        int res = 0, n = ratings.size();
        vector<int> dp(n, 1), dp2 = dp;
        for (int i = 1; i < n; ++i) {
            if (ratings[i] > ratings[i - 1]) dp[i] = dp[i - 1] + 1;
            else dp[i] = 1;
        }
        for (int i = n - 2; i >= 0; --i) {
            if (ratings[i] > ratings[i + 1]) dp2[i] = dp2[i + 1] + 1;
            else dp2[i] = 1;
        }
        for (int i = 0; i < n; ++i) {
            res += max(dp[i], dp2[i]);
        }
        return res;
    }
};