POJ 1470 Closest Common Ancestors - Tarjan

POJ 1470 Closest Common Ancestors

Wiki 上的 Tarjan 算法, Tarjan is an offline algorithm

http://en.wikipedia.org/wiki/Tarjan's_off-line_lowest_common_ancestors_algorithm

function TarjanOLCA(u)     MakeSet(u);     u.ancestor := u;     for each v in u.children do         TarjanOLCA(v);         Union(u,v);         Find(u).ancestor := u;     u.colour := black;     for each v such that {u,v} in P do         if v.colour == black             print "Tarjan's Lowest Common Ancestor of " + u +                   " and " + v + " is " + Find(v).ancestor + "."

然而我实现的与上面的稍微有些不同

function TarjanOLCA(u, ancestor)     MakeSet(u);     u.ancestor := u;     u.colour := black;     for each v such that {u,v} in P do         if v.colour == black             print "Tarjan's Lowest Common Ancestor of " + u +                   " and " + v + " is " + Find(v).ancestor + "."     for each v in u.children do          TarjanOLCA(v, u);      Find(u).ancestor := u;

Code for this problem:

#include <iostream>#include <cstring>#include <string>#include <cstdio>#include <vector>using namespace std;//Closet common ancestors//tarjan algorithmconst int N = 1000;vector<int> edges[N], query[N];int times[N];int fa[N];int find(int v) {  return v == fa[v]? v : fa[v] = find(fa[v]);}void tarjan(int v, int f) {  //cout<<"int tarjan:"<<v<<' '<<f<<endl;  fa[v] = v;  for (int i = 0; i < query[v].size(); ++i) {    int u = query[v][i];    if (fa[u] != -1) {      //u, v's closet common ancestor is find(u)      //cout<<u<<' '<<v<<" closet common ancestors is "<<find(u)<<endl;      times[find(u)]++;    }  }  for (int i = 0; i < edges[v].size(); ++i) {    int u = edges[v][i];    if (u == f) continue;    tarjan(u, v);  }  fa[v] = f;}int main(){  int n, q, a, b, c;  while (scanf("%d", &n) != EOF) {    memset(fa, 0, sizeof(int) * (n + 1));    for (int i = 1; i <= n; ++i) {      edges[i].clear();      query[i].clear();    }    //cout<<"start reading edge"<<endl;    for (int i = 1; i <= n; ++i) {      scanf("%d:(%d)", &a, &b);      while (b--) {        scanf("%d", &c);        //cout<<a<<' '<<c<<endl;        edges[a].push_back(c);        fa[c]++;      }    }    int r = -1;    for (int i = 1; i <= n; ++i) {      if (fa[i] == 0)        r = i;    }    scanf("%d", &q);    //cout<<"start reading query"<<endl;    for (int i = 0; i < q; ++i) {      scanf(" ( %d %d ) ", &a, &b);      //cout<<a<<' '<<b<<endl;      query[a].push_back(b);      query[b].push_back(a);    }    memset(times, 0, sizeof(int) * (n + 1));    memset(fa, -1, sizeof(int) * (n + 1));    tarjan(r, r);    for (int i = 1; i <= n; ++i) {      if (times[i])        printf("%d:%d\n", i, times[i]);    }  }  return 0;}