CF844A Diversity

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  • 题目来源 CodeForces 844A
  • 评测方式 RemoteJudge
  • 标签
  • 难度 省选/NOI-
  • 时空限制 1000ms / 256MB

题解

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    题意翻译

    给出一个字符串$S$与一个整数$k$。

    你可以更改$S$中的任意字符,使得字符串$S$中有不小于$k$个不同的字符。

    求最少的更改次数。

    $1\le k \le 26, 1\le |S|\le 1000.$

    题目描述

    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.

    输入输出格式

    输入格式:

    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 $ ).

    输出格式:

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

    输入输出样例

    输入样例#1: 复制
    yandex
    6
    
    输出样例#1: 复制
    0
    
    输入样例#2: 复制
    yahoo
    5
    
    输出样例#2: 复制
    1
    
    输入样例#3: 复制
    google
    7
    
    输出样例#3: 复制
    impossible
    

    说明

    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 $ .

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