【Codeforces 986B】Petr and Permutations

【链接】 我是链接,点我呀:)

【题意】

题意

【题解】

n为奇数时3*n和7*n+1奇偶性不同
n为偶数时也是如此
然后交换任意一对数
逆序对的对数的奇偶性会发生改变一次
求出逆序对 对n讨论得出答案。

【代码】

import java.io.*;
import java.util.*;

public class Main {

    static InputReader in;
    static PrintWriter out;

    public static void main(String[] args) throws IOException{
        //InputStream ins = new FileInputStream("E:\\rush.txt");
        InputStream ins = System.in;
        in = new InputReader(ins);
        out = new PrintWriter(System.out);
        //code start from here
        new Task().solve(in, out);
        out.close();
    }

    static int N = (int)1e6;
    static class Task{
        int n;
        int a[] = new int[N+10];
        int temp[] = new int[N+10];
        int ans = 0;

        public void mergesort(int l,int r) {
        	if (l>=r) return;
        	int mid = (l+r)/2;
        	mergesort(l,mid);mergesort(mid+1,r);
        	int k = l,i = l,j = mid+1;
        	while (i <= mid && j <= r) {
        		if (a[i]>a[j]) {
        			ans = ans + mid-i+1;
        			ans = ans % 2;
        			temp[k++] = a[j];
        			j++;
        		}else {
        			temp[k++] = a[i];
        			i++;
        		}
        	}
        	while (i<=mid) {
        		temp[k++] = a[i];
        		i++;
        	}
        	while (j<=r) {
        		temp[k++] = a[j];
        		j++;
        	}
        	for (i = l;i <= r;i++) a[i] = temp[i];

        }

        public void solve(InputReader in,PrintWriter out) {
        	n = in.nextInt();
        	for (int i = 1;i <= n;i++) {
        		a[i] = in.nextInt();
        	}
        	mergesort(1,n);
        	if (n%2==1) {
        		if (ans==1) {
        			out.println("Petr");
        		}else {
        			out.println("Um_nik");
        		}
        	}else {
        		if (ans==1) {
        			out.println("Um_nik");
        		}else {
        			out.println("Petr");
        		}
        	}
        }
    }

    static class InputReader{
        public BufferedReader br;
        public StringTokenizer tokenizer;

        public InputReader(InputStream ins) {
            br = new BufferedReader(new InputStreamReader(ins));
            tokenizer = null;
        }

        public String next(){
            while (tokenizer==null || !tokenizer.hasMoreTokens()) {
                try {
                tokenizer = new StringTokenizer(br.readLine());
                }catch(IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }
    }
}