B. Making a String
题目连接：
http://codeforces.com/contest/624/problem/B
Description
You are given an alphabet consisting of n letters, your task is to make a string of the maximum possible length so that the following conditions are satisfied:
the i-th letter occurs in the string no more than ai times;
the number of occurrences of each letter in the string must be distinct for all the letters that occurred in the string at least once.
Input
The first line of the input contains a single integer n (2 ≤ n ≤ 26) — the number of letters in the alphabet.
The next line contains n integers ai (1 ≤ ai ≤ 109) — i-th of these integers gives the limitation on the number of occurrences of the i-th character in the string.
Output
Print a single integer — the maximum length of the string that meets all the requirements.
Sample Input
3
2 5 5
Sample Output
11
Hint
题意
有n个字母，每个字母最多出现ai次，但是每个字母的出现次数都要求不一样
问你这个字符串最长多长
题解：
显然从大到小排序，然后贪心就好了，能选就选，不能选就--就行了
注意小心被减到负数了
代码
#include<bits/stdc++.h>
using namespace std;
int a[30];
map<int,int> H;
int main()
{
int n;scanf("%d",&n);
for(int i=1;i<=n;i++)
scanf("%d",&a[i]);
sort(a+1,a+1+n);
int flag = 0;
long long ans = 0;
for(int i=n;i>=1;i--)
{
int tmp = a[i];
while(H[tmp])tmp--;
if(tmp)
{
H[tmp]=1;
ans+=tmp;
}
}
cout<<ans<<endl;
}