codeforce_844A

本文介绍了一个编程挑战,目标是最少次数地改变字符串中的字符,以达到包含至少k个不同字母的要求。文章提供了示例输入输出,并解释了解决方案思路。

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Diversity
Time Limit: 1000msMemory Limit: 262144KB This problem will be judged on CodeForces. Original ID: 844A
64-bit integer IO format: %I64d Java class name: (Any)
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Calculate the minimum number of characters you need to change in the string s, so that it contains at least k different letters, or print that it is impossible.

String s consists only of lowercase Latin letters, and it is allowed to change characters only to lowercase Latin letters too.

Input
First line of input contains string s, consisting only of lowercase Latin letters (1 ≤ |s| ≤ 1000, |s| denotes the length of s).

Second line of input contains integer k (1 ≤ k ≤ 26).

Output
Print single line with a minimum number of necessary changes, or the word «impossible» (without quotes) if it is impossible.

Sample Input
Input
yandex
6
Output
0
Input
yahoo
5
Output
1
Input
google
7
Output
impossible
Hint
In the first test case string contains 6 different letters, so we don’t need to change anything.

In the second test case string contains 4 different letters: {‘a’, ‘h’, ‘o’, ‘y’}. To get 5 different letters it is necessary to change one occurrence of ‘o’ to some letter, which doesn’t occur in the string, for example, {‘b’}.

In the third test case, it is impossible to make 7 different letters because the length of the string is 6.

Source
AIM Tech Round 4 (Div. 2)

mean 看案例就能看懂把

#include<bits/stdc++.h>
using namespace std;
const int mm=1e9;
int main()
{
    char s[1111];
    int n,i,j;
    while(cin>>s>>n)
    {
        int len=strlen(s);
        set<char>  st;
        int cnt=0;
        for(i=0;i<len;i++)
        {
            if(st.find(s[i])==st.end())
                st.insert(s[i]);
            else cnt++;
        }
        int ans=st.size()+cnt;
        if(ans>=26)
            ans=26;
        if(ans<n)
            puts("impossible");
        else
        {
            if(n>st.size())
            cout<<n-st.size()<<endl;
            else puts("0");
        }

    }
}
### Codeforces Problem or Contest 998 Information For the specific details on Codeforces problem or contest numbered 998, direct references were not provided within the available citations. However, based on similar structures observed in other contests such as those described where configurations often include constraints like `n` representing numbers of elements with defined ranges[^1], it can be inferred that contest or problem 998 would follow a comparable format. Typically, each Codeforces contest includes several problems labeled from A to F or beyond depending on the round size. Each problem comes with its own set of rules, input/output formats, and constraint descriptions. For instance, some problems specify conditions involving integer inputs for calculations or logical deductions, while others might involve more complex algorithms or data processing tasks[^3]. To find detailed information regarding contest or problem 998 specifically: - Visit the official Codeforces website. - Navigate through past contests until reaching contest 998. - Review individual problem statements under this contest for precise requirements and examples. Additionally, competitive programming platforms usually provide comprehensive documentation alongside community discussions which serve valuable resources when exploring particular challenges or learning algorithmic solutions[^2]. ```cpp // Example C++ code snippet demonstrating how contestants interact with input/output during competitions #include <iostream> using namespace std; int main() { int n; cin >> n; // Process according to problem statement specifics } ```
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