地址:http://codeforces.com/problemset/problem/455/A
Alex doesn't like boredom. That's why whenever he gets bored, he comes up with games. One long winter evening he came up with a game and decided to play it.
Given a sequence a consisting of n integers. The player can make several steps. In a single step he can choose an element of the sequence (let's denote it ak) and delete it, at that all elements equal to ak + 1and ak - 1 also must be deleted from the sequence. That step brings ak points to the player.
Alex is a perfectionist, so he decided to get as many points as possible. Help him.
Input
The first line contains integer n (1 ≤ n ≤ 105) that shows how many numbers are in Alex's sequence.
The second line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 105).
Output
Print a single integer — the maximum number of points that Alex can earn.
Examples
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Output
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Note
Consider the third test example. At first step we need to choose any element equal to 2. After that step our sequence looks like this [2, 2, 2, 2]. Then we do 4 steps, on each step we choose any element equals to 2. In total we earn 10 points.
题意:删除ak,那么这个数组所有的ak+1,ak-1都被删除,同时得到ak分。求能得到的最大分数。
解析:对每个数进行了桶排序num。这样对后面的差大于1的数没有后效性。。从0位置开始向右消去,那么要消除一个数 i ,如果i-1被消去,那么i自然也不存在,此时dp[i] = dp[i-1],分数不变,因为i没得删。如果i-1没被删去,那么 dp[ i ] = dp[ i-2 ]+num[i]*i;