HDU2586

来源：互联网发布：阶级和阶层知乎编辑：程序博客网时间：2024/06/05 12:39
一道多次询问的最近公共祖先问题。
#include <iostream>#include <algorithm>#include <vector>#include <cstdio>#include <cstring>using namespace std;const int MAXN = 40000 + 10;struct Edge{   int to,cost;   Edge(){};   Edge(int _to,int _cost)      :to(_to),cost(_cost){};};vector<Edge> tree[MAXN];vector<Edge> Qes[MAXN];int degree[MAXN];int f[MAXN];bool vst[MAXN];int dist[MAXN];int ancestor[MAXN];int ans[MAXN];int rank[MAXN];int N,M;void init(){    for(int i = 0;i <= N;++i){        degree[i] = 0;        f[i] = i;        ans[i] = -1;        rank[i] = 0;        dist[i] = 0;        vst[i] = false;        ancestor[i] = -1;        tree[i].clear();        Qes[i].clear();    }}int Find(int x){    if(x == f[x])        return x;    return f[x] = Find(f[x]);}void LCA(int u){    int sz = tree[u].size();    for(int i = 0;i < sz;++i){        Edge& e = tree[u][i];        if(!vst[e.to]){            vst[e.to] = 1;            dist[e.to] = dist[u] + e.cost;            LCA(e.to);            f[e.to] = u;            int k = Qes[e.to].size();            for(int j = 0;j < k;++j){                Edge& et = Qes[e.to][j];                if(vst[et.to]&&ans[et.cost] == -1){  //还未遍历到                    if(et.to == e.to) ans[et.cost] = 0;                    else ans[et.cost] = dist[e.to] + dist[et.to] - 2*dist[Find(et.to)];                }            }        }    }}int main(){    int T;    scanf("%d",&T);    while(T--){        scanf("%d%d",&N,&M);        init();        int x,y,c;        for(int i = 1;i < N;++i){            scanf("%d%d%d",&x,&y,&c);            tree[x].push_back(Edge(y,c));            tree[y].push_back(Edge(x,c));        }        for(int i = 0;i < M;++i){            scanf("%d%d",&x,&y);            Qes[x].push_back(Edge(y,i));            Qes[y].push_back(Edge(x,i));        }        vst[1] = 1;        LCA(1);        for(int i = 0;i < M;++i){            printf("%d\n",ans[i]);        }    }    return 0;}
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