Graph2/TreeDiameter.hpp

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• Last update: 2023-07-17 18:02:31+09:00
• Include: #include "Graph2/TreeDiameter.hpp"

Depends on

• Graph2/GraphTemplate.hpp

Verified with

• test/yosupo_TreeDiameter.test.cpp

Code

#include "./GraphTemplate.hpp"

template<typename T>
pair<T,vector<int>> TreeDiameter(const Graph<T> &g){
    assert(g.V==g.E+1);
    vector<T> dis(g.V);
    vector<int> pre(g.V,-1);
    dis[0]=0;
    function<void(int,int)> dfs=[&g,&dfs,&dis,&pre](int par,int cur){
        for(auto &e:g[cur])if(par!=e.to){
            dis[e.to]=dis[cur]+e.w;
            pre[e.to]=cur;
            dfs(cur,e.to);
        }
    };
    dfs(-1,0);
    int l=max_element(ALL(dis))-begin(dis);
    dis[l]=0;
    pre.assign(g.V,-1);
    dfs(-1,l);
    int r=max_element(ALL(dis))-begin(dis);
    vector<int> path;
    for(int i=r;i!=-1;i=pre[i]) path.push_back(i);
    return make_pair(dis[r],path);
}

#line 1 "Graph2/GraphTemplate.hpp"



// graph template
// ref : https://ei1333.github.io/library/graph/graph-template.hpp
template<typename T=int>
struct Edge{
    int from,to;
    T w;
    int idx;
    Edge()=default;
    Edge(int from,int to,T w=1,int idx=-1):from(from),to(to),w(w),idx(idx){}
    operator int() const{return to;}
};

template<typename T=int>
struct Graph{
    vector<vector<Edge<T>>> g;
    int V,E;
    Graph()=default;
    Graph(int n):g(n),V(n),E(0){}

    int size(){
        return (int)g.size();
    }
    void resize(int k){
        g.resize(k);
        V=k;
    }
    inline const vector<Edge<T>> &operator[](int k)const{
        return (g.at(k));
    }
    inline vector<Edge<T>> &operator[](int k){
        return (g.at(k));
    }
    void add_directed_edge(int from,int to,T cost=1){
        g[from].emplace_back(from,to,cost,E++);
    }
    void add_edge(int from,int to,T cost=1){
        g[from].emplace_back(from,to,cost,E);
        g[to].emplace_back(to,from,cost,E++);
    }
    void read(int m,int pad=-1,bool weighted=false,bool directed=false){
        for(int i=0;i<m;i++){
            int u,v;cin>>u>>v;
            u+=pad,v+=pad;
            T w=T(1);
            if(weighted) cin>>w;
            if(directed) add_directed_edge(u,v,w);
            else         add_edge(u,v,w);
        }
    }
};


#line 2 "Graph2/TreeDiameter.hpp"

template<typename T>
pair<T,vector<int>> TreeDiameter(const Graph<T> &g){
    assert(g.V==g.E+1);
    vector<T> dis(g.V);
    vector<int> pre(g.V,-1);
    dis[0]=0;
    function<void(int,int)> dfs=[&g,&dfs,&dis,&pre](int par,int cur){
        for(auto &e:g[cur])if(par!=e.to){
            dis[e.to]=dis[cur]+e.w;
            pre[e.to]=cur;
            dfs(cur,e.to);
        }
    };
    dfs(-1,0);
    int l=max_element(ALL(dis))-begin(dis);
    dis[l]=0;
    pre.assign(g.V,-1);
    dfs(-1,l);
    int r=max_element(ALL(dis))-begin(dis);
    vector<int> path;
    for(int i=r;i!=-1;i=pre[i]) path.push_back(i);
    return make_pair(dis[r],path);
}

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