洛谷P2899 [USACO08JAN]手机网络Cell Phone Network

#include<bits/stdc++.h>#define N 100100using namespace std;const int INF=1008610086;int A[N],B[N],C[N];int beg[N],to[N],nex[N];int n,len;inline void Add(int a,int b){    nex[++len]=beg[a],beg[a]=len,to[len]=b;    nex[++len]=beg[b],beg[b]=len,to[len]=a;}void dfs(int p,int fa){    A[p]=B[p]=C[p]=0;int mib=1;int f=0;for(int i=beg[p];i;i=nex[i]){if(to[i]==fa) continue;dfs(to[i],p);if(A[to[i]]<=B[to[i]]){A[p]+=A[to[i]];mib=min(mib,B[to[i]]-A[to[i]]);}else A[p]+=B[to[i]],f=1;C[p]+=min(B[to[i]],A[to[i]]);B[p]+=min(C[to[i]],min(B[to[i]],A[to[i]]));}B[p]++;if(!f) A[p]+=mib;if(!A[p]) A[p]=1;}int main(){    scanf("%d",&n);    for(int i=1;i<n;i++){        int a,b;        scanf("%d%d",&a,&b);        Add(a,b);    }    dfs(1,0);    printf("%d\n",min(A[1],B[1]));    return 0;}