http://poj.org/problem?id=2631
2333水题,
有一个小技巧是说随便找一个点作为起点,
找到这个点的最远点,
以这个最远点为起点,
再次找到的最远点就是这个图的最远点
证明可以用三角形定理
#include<iostream> #include<cstdio> #include<vector> #include<cstring> #define maxn 10005 using namespace std; struct donser { int tow; int dis; }; vector<donser> vec[maxn]; int maxdistances=0,distances=0,maxtown=0; bool used[maxn]; void maxway(int x) { int way=vec[x].size(),i=0; struct donser a; //cout<<"?x:"<<x<<" vec[x].size():"<<way<<endl; while(i<way) { a=vec[x].at(i); i++; if(used[a.tow]) continue; distances+=a.dis; //cout<<"+a.dis:"<<a.dis<<endl; used[a.tow]=1; maxway(a.tow); if(distances>=maxdistances) { maxdistances=distances; maxtown=a.tow; } used[a.tow]=0; //cout<<"-a.dis:"<<a.dis<<endl; distances-=a.dis; } return; } int main() { int a,b,dist; struct donser num; //freopen("in.txt","r",stdin); while(~scanf("%d%d%d",&a,&b,&dist)) { num.tow=b; num.dis=dist; vec[a].push_back(num); num.tow=a; vec[b].push_back(num); } used[1]=1; maxway(1); distances=0; //cout<<"!maxtown"<<maxtown<<"!maxdistances"<<maxdistances<<endl; memset(used,0,sizeof(used)); maxway(maxtown); //cout<<"!maxtown"<<maxtown<<"!maxdistances"<<maxdistances<<endl; cout<<maxdistances<<endl; return 0; }