The 15th UESTC Programming Contest Preliminary J

地址：http://acm.uestc.edu.cn/#/problem/show/1567

题目：

Jermutat1on

Time Limit: 3000/1000MS (Java/Others)     Memory Limit: 65535/65535KB (Java/Others)

Submit Status

You are given two numbers nn and kk.

You are required to construct a permutation p1,p2,...,pnp1,p2,...,pn of numbers 1,2,...,n1,2,...,n such that there are exactly kk different numbers in |p1−p2||p1−p2|, |p2−p3||p2−p3|, ..., |pn−1−pn||pn−1−pn|.

Input

Only one line contains two integers nn and kk.

1≤k<n≤1000001≤k<n≤100000.

Output

Print nn integers forming the permutation.

If there are multiple answers, print any of them.

If there are no such permutation, print -1.

Sample input and output

Sample Input	Sample Output
3 1	1 2 3

Source

The 15th UESTC Programming Contest Preliminary

 思路：水题，见代码。

#include<iostream>
using namespace std;

int n,k;

int gcd(int x,int y)
{
    if(y==0)
        return x;
    else
        return gcd(y,x%y);
}

int main()
{
    cin>>n>>k;
    if(k>=n)
        cout<<-1<<endl;
    else
    {
        if(k==1)
            for(int i=1;i<=n;i++)
                cout<<i<<' ';
        else if(k%2)
        {
            int mid=(k+1)/2;
            cout<<mid<<' ';
            for(int i=1;i<=k;i++)
            {
                if(i%2)
                    cout<<(mid+=i)<<' ';
                else    
                    cout<<(mid-=i)<<' ';
            }
            for(int i=mid+1;i<=n;i++)
                cout<<i<<' ';
        }
        else
        {
            int mid=k/2+1;
            cout<<mid<<' ';
            for(int i=1;i<=k;i++)
            {
                if(i%2)
                    cout<<(mid-=i)<<' ';
                else    
                    cout<<(mid+=i)<<' ';
            }
            for(int i=mid+1;i<=n;i++)
                cout<<i<<' ';
        }
    }
    return 0;
}