A. Stages
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output
Natasha is going to fly to Mars. She needs to build a rocket, which consists of several stages in some order. Each of the stages is defined by a lowercase Latin letter. This way, the rocket can be described by the string — concatenation of letters, which correspond to the stages.
There are nn stages available. The rocket must contain exactly kk of them. Stages in the rocket should be ordered by their weight. So, after the stage with some letter can go only stage with a letter, which is at least two positions after in the alphabet (skipping one letter in between, or even more). For example, after letter 'c' can't go letters 'a', 'b', 'c' and 'd', but can go letters 'e', 'f', ..., 'z'.
For the rocket to fly as far as possible, its weight should be minimal. The weight of the rocket is equal to the sum of the weights of its stages. The weight of the stage is the number of its letter in the alphabet. For example, the stage 'a 'weighs one ton,' b 'weighs two tons, and'z' — 2626 tons.
Build the rocket with the minimal weight or determine, that it is impossible to build a rocket at all. Each stage can be used at most once.
Input
The first line of input contains two integers — nn and kk (1≤k≤n≤501≤k≤n≤50) – the number of available stages and the number of stages to use in the rocket.
The second line contains string ss, which consists of exactly nn lowercase Latin letters. Each letter defines a new stage, which can be used to build the rocket. Each stage can be used at most once.
Output
Print a single integer — the minimal total weight of the rocket or -1, if it is impossible to build the rocket at all.
Examples
input
Copy
5 3 xyabd
output
Copy
29
input
Copy
7 4 problem
output
Copy
34
input
Copy
2 2 ab
output
Copy
-1
input
Copy
12 1 abaabbaaabbb
output
Copy
1
Note
In the first example, the following rockets satisfy the condition:
- "adx" (weight is 1+4+24=291+4+24=29);
- "ady" (weight is 1+4+25=301+4+25=30);
- "bdx" (weight is 2+4+24=302+4+24=30);
- "bdy" (weight is 2+4+25=312+4+25=31).
Rocket "adx" has the minimal weight, so the answer is 2929.
In the second example, target rocket is "belo". Its weight is 2+5+12+15=342+5+12+15=34.
In the third example, n=k=2n=k=2, so the rocket must have both stages: 'a' and 'b'. This rocket doesn't satisfy the condition, because these letters are adjacent in the alphabet. Answer is -1.
题意：建造一枚火箭分成很多阶段，每个阶段由一个字母构成，让你在n阶段里面选择k个字母，让k个字母和的asc码值最小。但是满足规则，选了当前字母后，下一个字母不能比前一个小，也不能相邻前一个字母，选c,下一个不能选a,b,c，和d。
题解：贪心 先把n个字母排序，从第一个选，下一个字母判断asc差值是否大于1，然后记录当前选的字母。
c++：
#include<bits/stdc++.h>
using namespace std;
int main()
{
int n,k,ans=0;
char last;
string s;
cin>>n>>k>>s;
sort(s.begin(),s.end());
ans+=s[0]-'a'+1,k--;
last=s[0];
for(int i=1; i<n; i++)
{
if(k==0) break;
if(s[i]-last>1) ans+=s[i]-'a'+1,k--,last=s[i];
}
if(k) cout<<-1<<endl;
else cout<<ans<<endl;
return 0;
}python：
n,k=map(int,input().split())
ans=x=0
for i in sorted(map(ord,input())):
if i-x>1:
ans+=i-96
x=i
k-=1
if k==0: break
if k>0: print(-1)
else: print(ans)