CodeForces 673D Bear and Two Paths（构造）

思路：构造，显然是一个蝴蝶形状的图

#include<bits\stdc++.h>
using namespace std;

int main()
{
int n,k,a,b,c,d;
vector<int>g;
scanf("%d%d",&n,&k);
scanf("%d%d%d%d",&a,&b,&c,&d);
if(n==4)
{
puts("-1");
return 0;
}
if (k<=n)
{
puts("-1");
return 0;
}
for (int i = 1;i<=n;i++)
{
if(i==a||i==b||i==c||i==d)
continue;
g.push_back(i);
}
printf("%d %d ",a,c);
for (int i = 0;i<g.size();i++)
printf("%d ",g[i]);
printf("%d %d\n",d,b);
printf("%d %d ",c,a);
for (int i = 0;i<g.size();i++)
printf("%d ",g[i]);
printf("%d %d\n",b,d);
}

Description

Bearland has n cities, numbered 1 through n. Cities are connected via
bidirectional roads. Each road connects two distinct cities. No two roads connect the same pair of cities.

Bear Limak was once in a city a and he wanted to go to a city b. There was no direct connection so he decided to take a long
walk, visiting each city exactly once. Formally:

There is no road between a and b.
There exists a sequence (path) of n distinct cities v1, v2, ..., vn that v1 = a, vn = b and
there is a road between vi and vi + 1 for

.

On the other day, the similar thing happened. Limak wanted to travel between a city c and a city d. There is no road between
them but there exists a sequence of n distinct cities u1, u2, ..., un that u1 = c, un = d and
there is a road between ui and ui + 1 for

.

Also, Limak thinks that there are at most k roads in Bearland. He wonders whether he remembers everything correctly.

Given n, k and four distinct cities a, b, c, d,
can you find possible paths (v1, ..., vn) and (u1, ..., un) to
satisfy all the given conditions? Find any solution or print -1 if it's impossible.

Input

The first line of the input contains two integers n and k (4 ≤ n ≤ 1000, n - 1 ≤ k ≤ 2n - 2) —
the number of cities and the maximum allowed number of roads, respectively.

The second line contains four distinct integers a, b, c and d (1 ≤ a, b, c, d ≤ n).

Output

Print -1 if it's impossible to satisfy all the given conditions. Otherwise, print two lines with paths descriptions. The first of these two lines should contain n distinct
integers v1, v2, ..., vn where v1 = a and vn = b.
The second line should contain n distinct integersu1, u2, ..., un where u1 = c and un = d.

Two paths generate at most 2n - 2 roads: (v1, v2), (v2, v3), ..., (vn - 1, vn), (u1, u2), (u2, u3), ..., (un - 1, un).
Your answer will be considered wrong if contains more than k distinct roads or any other condition breaks. Note that (x, y) and (y, x) are
the same road.

Sample Input

Input

7 11
2 4 7 3

Output

2 7 1 3 6 5 4
7 1 5 4 6 2 3

Input

1000 999
10 20 30 40

Output

-1