A:樹遍歷 DFS 貪心 先從最遠的點開始判

如果某個點連有的算上自身的junction不小於二就ans++ return 0

連有的算上自身的junction為一 就return 1

#include <bits/stdc++.h>
#include <cstring>
#include <iostream>
#include <algorithm>
#define INF 0x3f3f3f3f
#define MOD 1000000007
#define mem(a,b) memset((a),b,sizeof(a))
#define TS printf("!!!\n")
#define
 
 pb push_back
#define pai pair<int,int>
#define mid ((l+r)/2)
#define lson l,mid,(rt<<1)
#define rson mid+1,r,(rt<<1|1)
//ugooo ll = long long;
//ugooo ull= unsigned long long;
//std::ios::sync_with_stdio(false);
using namespace std;
//priority_queue<int,vector<int>,greater<int>> que;
 

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pairint;
const double eps=1e-8;
const double PI=acos(-1);
const ll INFLL = 0x3f3f3f3f3f3f3f3fLL;
const int maxn=200005;
vector<int> t[maxn];
int a[maxn],f[maxn];
int ans=0;
void dfs(int x,int pre)
{
 int sum=0;
 int len=t[x].size();
 
 
for(int i=0;i<len;i++)
 {
        int aim=t[x][i];
        if(aim==pre)
                continue;
        dfs(aim,x);
        sum+=a[aim];
 }
 sum+=f[x];
 if(sum>=2)
 {
        ans++;
        a[x]=0;
 }
 else if(sum==1)
 a[x]=1;
 else
 a[x]=0;
}
int main()
{
        int n;
        cin >> n ;
        int from,to;
        for(int i=1;i<n;i++)
        {
        scanf("%d %d",&from,&to);
        t[from].pb(to);
        t[to].pb(from);
        }
        int m;
        cin >> m ;
        int now;
        for(int i=1;i<=m;i++)
        {
        scanf("%d",&now);
        f[now]=1;
        }
        dfs(1,-1);
        for(int i=1;i<=n;i++)
        cout<<a[i]<<" ";
        cout<<endl;
        cout<<ans<<endl;
    return 0;
}

B;SPFA

C:爆搜

D:並查集

E:模擬

Summer training round2 #6 (Training #26)