1907: 树的路径覆盖 贪心

从底向上，能合并就合并，标记一下经过根节点的路径是哪种路径（就两种很好yy）。

#include<iostream>#include<cstdio>#include<cstring>using namespace std;int n,cnt,T;int head[10005],list[20005],next[20005];int f[10005],v[10005];inline int read(){    int a=0,f=1; char c=getchar();    while (c<'0'||c>'9') {if (c=='-') f=-1; c=getchar();}    while (c>='0'&&c<='9') {a=a*10+c-'0'; c=getchar();}    return a*f;}inline void insert(int x,int y){    next[++cnt]=head[x];    head[x]=cnt;    list[cnt]=y;}void dfs(int x,int fa){    int tmp=0;    f[x]=1;    for (int i=head[x];i;i=next[i])        if (list[i]!=fa)        {            dfs(list[i],x);            f[x]+=f[list[i]];            if (!v[list[i]]) tmp++;        }    if (tmp>=2) f[x]-=2,v[x]=1;    else if (tmp==1) f[x]--;}int main(){    T=read();    while (T--)    {        n=read(); cnt=0;        memset(head,0,sizeof(head));        memset(f,0,sizeof(f));        memset(v,0,sizeof(v));        for (int i=1;i<n;i++)        {            int u=read(),v=read();            insert(u,v); insert(v,u);        }        dfs(1,0);        printf("%d\n",f[1]);    }    return 0;}