C. Bear and Forgotten Tree 3
time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

A tree is a connected undirected graph consisting of n vertices and n  -  1 edges. Vertices are numbered 1 through n.

Limak is a little polar bear and Radewoosh is his evil enemy. Limak once had a tree but Radewoosh stolen it. Bear is very sad now because he doesn't remember much about the tree — he can tell you only three values nd and h:

  • The tree had exactly n vertices.
  • The tree had diameter d. In other words, d was the biggest distance between two vertices.
  • Limak also remembers that he once rooted the tree in vertex 1 and after that its height was h. In other words, h was the biggest distance between vertex 1 and some other vertex.

The distance between two vertices of the tree is the number of edges on the simple path between them.

Help Limak to restore his tree. Check whether there exists a tree satisfying the given conditions. Find any such tree and print its edges in any order. It's also possible that Limak made a mistake and there is no suitable tree – in this case print "-1".

Input

The first line contains three integers nd and h (2 ≤ n ≤ 100 000, 1 ≤ h ≤ d ≤ n - 1) — the number of vertices, diameter, and height after rooting in vertex 1, respectively.

Output

If there is no tree matching what Limak remembers, print the only line with "-1" (without the quotes).

Otherwise, describe any tree matching Limak's description. Print n - 1 lines, each with two space-separated integers – indices of vertices connected by an edge. If there are many valid trees, print any of them. You can print edges in any order.

Examples
input
5 3 2
output
1 2
1 3
3 4
3 5
input
8 5 2
output
-1
input
8 4 2
output
4 8
5 7
2 3
8 1
2 1
5 6
1 5
Note

Below you can see trees printed to the output in the first sample and the third sample.

构造。

每次先以1为根构造深度为h的一支树杈1-2-3...h,如果h==d那么就在2下面接上1个节点 如果h!=d 那么就在1下面接上d-h个节点。

注意h==d的时候。2 1 1是有解的。

/* ***********************************************
Author :guanjun
Created Time :2016/3/29 9:49:51
File Name :cfvk1c.cpp
************************************************ */
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <iomanip>
#include <list>
#include <deque>
#include <stack>
#define ull unsigned long long
#define ll long long
#define mod 90001
#define INF 0x3f3f3f3f
#define maxn 100010
#define cle(a) memset(a,0,sizeof(a))
const ull inf = 1LL << ;
const double eps=1e-;
using namespace std;
priority_queue<int,vector<int>,greater<int> >pq;
struct Node{
int x,y;
};
struct cmp{
bool operator()(Node a,Node b){
if(a.x==b.x) return a.y> b.y;
return a.x>b.x;
}
}; bool cmp(int a,int b){
return a>b;
}
vector<int>v[maxn];
int main()
{
#ifndef ONLINE_JUDGE
//freopen("in.txt","r",stdin);
#endif
//freopen("out.txt","w",stdout);
int n,d,h;
while(cin>>n>>d>>h){
if(d>h*){
puts("-1");continue;
}
int num=;
int vec,w;
if(d==h){
if(h==&&n>){
cout<<-<<endl;continue;
}
vec=,w=d-h+;
}
else vec=,w=d-h;
for(int i=;i<=h;i++){
v[num].push_back(num+);
num++;
}
for(int i=;i<=d-h;i++){
if(i==)v[vec].push_back(num+);
else v[num].push_back(num+);
num++;
//puts("-1");
}
//cout<<"num "<<num<<endl;
int mark=;
while(){
if(num==n)break;
for(int i=;i<=w;i++){
if(i==)v[vec].push_back(num+);
else v[num].push_back(num+);
num++;
if(num==n){
mark=;break;
}
}
if(mark)break;
}
for(int i=;i<=n;i++){
for(int j=;j<v[i].size();j++){
cout<<i<<" "<<v[i][j]<<endl;
}
}
}
return ;
}
C. Bear and Forgotten Tree 3
time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

A tree is a connected undirected graph consisting of n vertices and n  -  1 edges. Vertices are numbered 1 through n.

Limak is a little polar bear and Radewoosh is his evil enemy. Limak once had a tree but Radewoosh stolen it. Bear is very sad now because he doesn't remember much about the tree — he can tell you only three values nd and h:

  • The tree had exactly n vertices.
  • The tree had diameter d. In other words, d was the biggest distance between two vertices.
  • Limak also remembers that he once rooted the tree in vertex 1 and after that its height was h. In other words, h was the biggest distance between vertex 1 and some other vertex.

The distance between two vertices of the tree is the number of edges on the simple path between them.

Help Limak to restore his tree. Check whether there exists a tree satisfying the given conditions. Find any such tree and print its edges in any order. It's also possible that Limak made a mistake and there is no suitable tree – in this case print "-1".

Input

The first line contains three integers nd and h (2 ≤ n ≤ 100 000, 1 ≤ h ≤ d ≤ n - 1) — the number of vertices, diameter, and height after rooting in vertex 1, respectively.

Output

If there is no tree matching what Limak remembers, print the only line with "-1" (without the quotes).

Otherwise, describe any tree matching Limak's description. Print n - 1 lines, each with two space-separated integers – indices of vertices connected by an edge. If there are many valid trees, print any of them. You can print edges in any order.

Examples
input
5 3 2
output
1 2
1 3
3 4
3 5
input
8 5 2
output
-1
input
8 4 2
output
4 8
5 7
2 3
8 1
2 1
5 6
1 5
Note

Below you can see trees printed to the output in the first sample and the third sample.

VK Cup 2016 - Round 1 (Div. 2 Edition) C. Bear and Forgotten Tree 3的更多相关文章

  1. VK Cup 2016 - Round 1 (Div. 2 Edition) C. Bear and Forgotten Tree 3 构造

    C. Bear and Forgotten Tree 3 题目连接: http://www.codeforces.com/contest/658/problem/C Description A tre ...

  2. Codeforces Round #351 (VK Cup 2016 Round 3, Div. 2 Edition) D Bear and Two Paths

    题目链接: http://codeforces.com/contest/673/problem/D 题意: 给四个不同点a,b,c,d,求是否能构造出两条哈密顿通路,一条a到b,一条c到d. 题解: ...

  3. Codeforces Round #351 (VK Cup 2016 Round 3, Div. 2 Edition) C - Bear and Colors

    题目链接: http://codeforces.com/contest/673/problem/C 题解: 枚举所有的区间,维护一下每种颜色出现的次数,记录一下出现最多且最小的就可以了. 暴力n*n. ...

  4. Codeforces Round #351 (VK Cup 2016 Round 3, Div. 2 Edition) D. Bear and Two Paths 构造

    D. Bear and Two Paths 题目连接: http://www.codeforces.com/contest/673/problem/D Description Bearland has ...

  5. Codeforces Round #351 (VK Cup 2016 Round 3, Div. 2 Edition) C. Bear and Colors 暴力

    C. Bear and Colors 题目连接: http://www.codeforces.com/contest/673/problem/C Description Bear Limak has ...

  6. Codeforces Round #351 (VK Cup 2016 Round 3, Div. 2 Edition) A. Bear and Game 水题

    A. Bear and Game 题目连接: http://www.codeforces.com/contest/673/problem/A Description Bear Limak likes ...

  7. VK Cup 2016 - Round 1 (Div. 2 Edition) E. Bear and Contribution 单调队列

    E. Bear and Contribution 题目连接: http://www.codeforces.com/contest/658/problem/E Description Codeforce ...

  8. VK Cup 2016 - Round 1 (Div. 2 Edition) D. Bear and Polynomials

    D. Bear and Polynomials 题目连接: http://www.codeforces.com/contest/658/problem/D Description Limak is a ...

  9. VK Cup 2016 - Round 1 (Div. 2 Edition) B. Bear and Displayed Friends 树状数组

    B. Bear and Displayed Friends 题目连接: http://www.codeforces.com/contest/658/problem/B Description Lima ...

随机推荐

  1. 【HDOJ5980】Find Small A(签到)

    题意:不知道 思路:队友写的 #include <stdio.h> #include <vector> #include <algorithm> #include ...

  2. Linux上安装使用SSH

    參考博客:http://blog.csdn.net/xqhrs232/article/details/50960520 Ubuntu安装使用SSH ubuntu默认并没有安装ssh服务,如果通过ssh ...

  3. cobbler api接口开发测试实例

    条件1:必须搭建好cobbler服务,并且可以通过web访问:http://cobbler_ip/cobbler_web 测试可以打开.然后再用以下命令测试. #!/opt/python3/bin/p ...

  4. luogu P2296 寻找道路

    题目描述 在有向图G 中,每条边的长度均为1 ,现给定起点和终点,请你在图中找一条从起点到终点的路径,该路径满足以下条件: 1 .路径上的所有点的出边所指向的点都直接或间接与终点连通. 2 .在满足条 ...

  5. Codeforces 735 E Ostap and Tree

    Discription Ostap already settled down in Rio de Janiero suburb and started to grow a tree in his ga ...

  6. systemtap-note-6-userspace-stack-backtrace

    http://nanxiao.me/systemtap-note-6-userspace-stack-backtrace/

  7. Angular 路由⑦要素

    cnzt       http://www.cnblogs.com/zt-blog/p/7919185.html http://www.cnblogs.com/zt-blog/p/7919185.ht ...

  8. Android 集成支付宝支付详解

    一说到支付宝,相信没有人不知道,生活中付款,转账都会用到. 今天来详细介绍下在Android中如何集成支付宝支付到自己的APP中去.让APP能够拥有方便,快捷的支付功能. 准备工作: 商户在b.ali ...

  9. 项目整理--Echarts前端后台的贯通写法

    项目整理–Echarts前端后台的贯通写法 注:下面所有内容建立在FH admin开源框架和eharts插件基础上,建议观看本案例者进行了解. 业务逻辑 绘制两张图表.分别显示城市空间库和其它数据仓库 ...

  10. 【Android小项目】找不同,改编自&quot;寻找房祖名&quot;的一款开源小应用。

    近期在微信朋友圈"寻找房祖名"和"万里寻刀"这类小游戏比較火.我试着写了一个android版本号的,里面全是一系列的形近字,实现原理非常easy:用一个Grid ...