CF939A Love Triangle

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  • 题目来源 CodeForces 939A
  • 评测方式 RemoteJudge
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  • 难度 入门难度
  • 时空限制 1000ms / 256MB

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    题意翻译

    题目描述

    飞机跟人一样,也会有三角恋。现在有$n$ 架飞机,编号从1~$n$ ,且第$i$ 号飞机喜欢$f_{i}$ 号飞机,且1<=$f_{i}$ <=$n$ ,$f_{i}$ ≠$i$ 。 当飞机$A$ 喜欢飞机$B$ ,且飞机$B$ 喜欢飞机$C$ ,且飞机$C$ 喜欢飞机$A$ ,我们称这种情况为三角恋。 现在请你找出是否存在三角恋。

    输入输出格式

    输入格式

    第一行一个数,飞机的个数$n$ ,且$1&lt;=n&lt;=5000$
    第二行$n$ 个数,$f_{1},f_{2},...,f_{n}$ ,代表$i$ 号飞机喜欢$f_{i}$ 号飞机

    输出格式

    如果存在三角恋则输出"YES",否则输出“NO” 输出大小写都没问题

    题目描述

    As you could know there are no male planes nor female planes. However, each plane on Earth likes some other plane. There are $ n $ planes on Earth, numbered from $ 1 $ to $ n $ , and the plane with number $ i $ likes the plane with number $ f_{i} $ , where $ 1<=f_{i}<=n $ and $ f_{i}≠i $ .

    We call a love triangle a situation in which plane $ A $ likes plane $ B $ , plane $ B $ likes plane $ C $ and plane $ C $ likes plane $ A $ . Find out if there is any love triangle on Earth.

    输入输出格式

    输入格式:

    The first line contains a single integer $ n $ ( $ 2<=n<=5000 $ ) — the number of planes.

    The second line contains $ n $ integers $ f_{1},f_{2},...,f_{n} $ ( $ 1<=f_{i}<=n $ , $ f_{i}≠i $ ), meaning that the $ i $ -th plane likes the $ f_{i} $ -th.

    输出格式:

    Output «YES» if there is a love triangle consisting of planes on Earth. Otherwise, output «NO».

    You can output any letter in lower case or in upper case.

    输入输出样例

    输入样例#1: 复制
    5
    2 4 5 1 3
    
    输出样例#1: 复制
    YES
    
    输入样例#2: 复制
    5
    5 5 5 5 1
    
    输出样例#2: 复制
    NO
    

    说明

    In first example plane $ 2 $ likes plane $ 4 $ , plane $ 4 $ likes plane $ 1 $ , plane $ 1 $ likes plane $ 2 $ and that is a love triangle.

    In second example there are no love triangles.

    提示
    标程仅供做题后或实在无思路时参考。
    请自觉、自律地使用该功能并请对自己的学习负责。
    如果发现恶意抄袭标程,将按照I类违反进行处理。