codeforces 986B Petr and Permutations

http://www.elijahqi.win/archives/3560
Petr likes to come up with problems about randomly generated data. This time problem is about random permutation. He decided to generate a random permutation this way: he takes identity permutation of numbers from 1

1
to n

n
and then 3n

3n
times takes a random pair of different elements and swaps them. Alex envies Petr and tries to imitate him in all kind of things. Alex has also come up with a problem about random permutation. He generates a random permutation just like Petr but swaps elements 7n+1

7n+1
times instead of 3n

3n
times. Because it is more random, OK?!

You somehow get a test from one of these problems and now you want to know from which one.

Input
In the first line of input there is one integer n

n
(103≤n≤106

103≤n≤106
).

In the second line there are n

n
distinct integers between 1

1
and n

n
— the permutation of size n

n
from the test.

It is guaranteed that all tests except for sample are generated this way: First we choose n

n
— the size of the permutation. Then we randomly choose a method to generate a permutation — the one of Petr or the one of Alex. Then we generate a permutation using chosen method.

Output
If the test is generated via Petr’s method print “Petr” (without quotes). If the test is generated via Alex’s method print “Um_nik” (without quotes).

Example
input

Copy
5
2 4 5 1 3
output

Copy
Petr
Note
Please note that the sample is not a valid test (because of limitations for n

n
) and is given only to illustrate input/output format. Your program still has to print correct answer to this test to get AC.

Due to randomness of input hacks in this problem are forbidden.

大爷题解

https://blog.youkuaiyun.com/icefox_zhx/article/details/80520051

#include<cstdio>
#include<cctype>
#include<algorithm>
#define ll long long
using namespace std;
inline char gc(){
    static char now[1<<16],*S,*T;
    if (T==S){T=(S=now)+fread(now,1,1<<16,stdin);if (T==S) return EOF;}
    return *S++;
}
inline int read(){
    int x=0,f=1;char ch=gc();
    while(!isdigit(ch)) {if (ch=='-') f=-1;ch=gc();}
    while(isdigit(ch)) x=x*10+ch-'0',ch=gc();
    return x*f;
}
const int N=1e6+10;
int s[N],n,a[N];ll ans;
inline void add(int x,int v){
    while(x<=n) s[x]+=v,x+=x&-x;
}
inline int query(int x){
    ll tmp=0;
    while(x) tmp+=s[x],x-=x&-x;return tmp;
}
int main(){
//  freopen("e.in","r",stdin);
    n=read();
    for (int i=1;i<=n;++i) a[i]=read();
    for (int i=n;i;--i){
        ans+=query(a[i]);
        add(a[i],1);
    }
    ans&=1;n&=1;
    if (ans==n) puts("Petr");
    else puts("Um_nik");
    return 0;
}