【PAT】【Advanced Level】1021. Deepest Root (25)

最新推荐文章于 2022-03-06 17:13:01 发布

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最新推荐文章于 2022-03-06 17:13:01 发布

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本文介绍了一种算法，用于在给定的连通无环图（树）中找到能够生成最高树形结构的根节点。通过两次深度优先搜索确定所有最深根节点，并处理非树形图的情况。

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1021. Deepest Root (25)

时间限制

1500 ms

内存限制

65536 kB

代码长度限制

16000 B

判题程序

Standard

作者

CHEN, Yue

A graph which is connected and acyclic can be considered a tree. The height of the tree depends on the selected root. Now you are supposed to find the root that results in a highest tree. Such a root is called the deepest root.

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer N (<=10000) which is the number of nodes, and hence the nodes are numbered from 1 to N. Then N-1 lines follow, each describes an edge by given the two adjacent nodes' numbers.

Output Specification:

For each test case, print each of the deepest roots in a line. If such a root is not unique, print them in increasing order of their numbers. In case that the given graph is not a tree, print "Error: K components" where K is the number of connected components in the graph.

Sample Input 1:

Sample Output 1:

3
4
5

Sample Input 2:

Sample Output 2:

Error: 2 components

原题链接：

https://www.patest.cn/contests/pat-a-practise/1021

https://www.nowcoder.com/questionTerminal/f793ad2e0c7344efa8b6c18d10d4b67b

思路：

参见牛客网。。

好坑。。

CODE：

#include<iostream>
#include<vector>
#include<cstring>
#include<algorithm>
#define N 10010
using namespace std;
vector<int> dist[N];
int gs;
bool fl[N];
int n;
int maxx=0;
int maxn;
int re[N];
int re1[N];
int num1=0;
int nnum1;
void dfs(int no,int flo)
{
    if (flo>=maxx)
    {
        if (flo>maxx) num1=0;
        maxx=flo;
        re[num1]=no;
        num1++;
    }
    int gs=0;
    if(dist[no].empty()) return ;
    for (int i=0;i<dist[no].size();i++)
    {
        if (fl[dist[no][i]]==1) continue;
        fl[dist[no][i]]=1;
        dfs(dist[no][i],flo+1);
    }
    return;
}
bool cmp(int a,int b)
{
    return a<b;
}
int main()
{
    memset(fl,0,sizeof(fl));
    cin>>n;
    for(int i=0;i<n-1;i++)
    {
        int u,v;
        cin>>u>>v;
        u--;
        v--;
        dist[v].push_back(u);
        dist[u].push_back(v);
    }
    gs=0;
    for (int i=0;i<n;i++)
    {
        if (fl[i]==0)
        {
            fl[i]=1;
            gs++;
            dfs(i,0);
        }
    }
    if (gs>1)
    {
        cout<<"Error: "<<gs<<" components";
    }
    else
    {
        memset(fl,0,sizeof(fl));
        for (int i=0;i<num1;i++)
        {
            re1[i]=re[i];
        }
        int nnn=num1;
        num1=0;
        maxx=0;
        dfs(re[0],0);
        for (int i=0;i<num1;i++)
        {
            re1[nnn+i]=re[i];
        }
        nnn+=num1;
        sort(re1,re1+nnn,cmp);
        for (int i=0;i<nnn;i++)
            if (i==0 || re1[i]!=re1[i-1])cout<<re1[i]+1<<endl;
    }
    return 0;
}