zoukankan      html  css  js  c++  java
  • Codeforces Round #397 E题Tree Folding(BFS)解题报告

    E. Tree Folding
    time limit per test
    2 seconds
    memory limit per test
    512 megabytes
    input
    standard input
    output
    standard output

    Vanya wants to minimize a tree. He can perform the following operation multiple times: choose a vertex v, and two disjoint (except for v) paths of equal length a0 = va1, ..., ak, and b0 = vb1, ..., bk. Additionally, vertices a1, ..., akb1, ..., bk must not have any neighbours in the tree other than adjacent vertices of corresponding paths. After that, one of the paths may be merged into the other, that is, the vertices b1, ..., bk can be effectively erased:

    Help Vanya determine if it possible to make the tree into a path via a sequence of described operations, and if the answer is positive, also determine the shortest length of such path.

    Input

    The first line of input contains the number of vertices n (2 ≤ n ≤ 2·105).

    Next n - 1 lines describe edges of the tree. Each of these lines contains two space-separated integers u and v (1 ≤ u, v ≤ nu ≠ v) — indices of endpoints of the corresponding edge. It is guaranteed that the given graph is a tree.

    Output

    If it is impossible to obtain a path, print -1. Otherwise, print the minimum number of edges in a possible path.

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

    In the first sample case, a path of three edges is obtained after merging paths 2 - 1 - 6 and 2 - 4 - 5.

    It is impossible to perform any operation in the second sample case. For example, it is impossible to merge paths 1 - 3 - 4 and 1 - 5 - 6, since vertex 6 additionally has a neighbour 7 that is not present in the corresponding path.

    从每个叶结点开始走。如果某点连的不同子长度个数大于等于3则不存在。

     1 #include <iostream>
     2 #include<bits/stdc++.h>
     3 #include <queue>
     4 #include <cstdio>
     5 #include <cstring>
     6 #include <algorithm>
     7 using namespace std;
     8 typedef long long ll;
     9 typedef unsigned long long ull;
    10 const int MAX=2e5+5;
    11 set <int> edge[MAX];
    12 set <int> dis[MAX];
    13 queue <int> que;
    14 bool vi[MAX];
    15 int re(int x)
    16 {
    17     while(x%2==0)
    18         x/=2;
    19     return x;
    20 }
    21 int solve()
    22 {
    23     memset(vi,false,sizeof(vi));
    24     while(!que.empty())
    25     {
    26         int u=que.front();
    27         que.pop();
    28         if(vi[u])
    29             continue;
    30         if(edge[u].size()==1)
    31         {
    32             if(dis[u].size()==1)
    33             {
    34                 int v=*edge[u].begin();
    35                 edge[u].erase(v);
    36                 edge[v].erase(u);
    37                 dis[v].insert(*dis[u].begin()+ 1 );
    38                 que.push(v);
    39                 vi[u]=true;
    40             }
    41         }
    42         else if(edge[u].empty())
    43         {
    44             if(dis[u].size()>=3)
    45             {
    46                 return -1;
    47             }
    48             if(dis[u].size()==1)
    49                 return re(*dis[u].begin());
    50             return re(*dis[u].begin()+*dis[u].rbegin());
    51 
    52         }
    53 
    54     }
    55     return -1;
    56 }
    57 int n;
    58 int main()
    59 {
    60     scanf("%d",&n);
    61     int i;
    62     int u,v;
    63     for(i=1;i<=n-1;i++)
    64     {
    65         scanf("%d %d",&u,&v);
    66         edge[u].insert(v);
    67         edge[v].insert(u);
    68     }
    69     for(i=1;i<=n;i++)
    70     {
    71         if(edge[i].size()==1)
    72         {
    73             que.push(i);
    74             dis[i].insert(0);
    75         }
    76     }
    77     printf("%d
    ",solve());
    78 }
  • 相关阅读:
    ES基本介绍
    Mybatis 读写分离简单实现
    分享一个Flink checkpoint失败的问题和解决办法
    一次“内存泄露”引发的血案
    记一次堆外内存泄漏排查过程
    MySQL主从复制读写分离,看这篇就够了!
    JVM运行时内存数据区域
    .NET MVC 页面传值方式
    jQuery 对表格内容进行搜索筛选
    泛型
  • 原文地址:https://www.cnblogs.com/quintessence/p/6399618.html
Copyright © 2011-2022 走看看