poj 1330 Nearest Common Ancestors

LCA 测板子的题

学会了倍增

#include<cstring>#include<cstdio>#include<vector>#include<algorithm>using namespace std;const int maxn = 112345,maxm = 112345,max_log = 17;const int ROOT = 1;int deep[maxn],fa[maxn][max_log];int nofa[maxn];struct Edge{    struct Node{        int nex,to;        Node(int nex=0,int to=0):nex(nex),to(to){};    };    Node node[maxm];    int head[maxn],top;    void init(){        memset(head,-1,sizeof(head));        top = 0;    }    void Link(int st,int ed){        node[top] = Node(head[st],ed);        head[st] = top++;    }    int Start(int st){ return head[st]; }    void Next(int &st){ st = node[st].nex; }    int To(int st){ return node[st].to; }}edge;int getroot(int n){    for(int i=1;i<=n;i++){        if(nofa[i] == -1) return i;    }    return -1;}void dfs(int st,int Fa,int Deep=1){    for(int i=1;i<max_log;i++)        fa[st][i] = -1;    fa[st][0] = Fa,deep[st] = Deep;    for(int i = edge.Start(st);i != -1;edge.Next(i)){         if(edge.To(i) == Fa) continue;        dfs(edge.To(i),st,Deep+1);    }}void init(int n){    memset(fa,-1,sizeof(fa));    dfs(getroot(n),-1);    for (int j = 1;j < max_log;j++){        for (int i = 1;i <= n;i++){            if (fa[i][j-1] != -1){                fa[i][j] = fa[fa[i][j-1]][j-1];            }        }    }}int lca(int x,int y){    if (deep[x] < deep[y]) swap(x,y);    for (int i = max_log-1;i >= 0;i--){        if (deep[fa[x][i]] >= deep[y]){            x = fa[x][i];        }    }    if (x == y) return x;     for (int i = max_log-1;i >= 0;i--){        if (fa[x][i] != fa[y][i]){            x = fa[x][i];             y = fa[y][i];        }    }    return fa[x][0];}int main(){    int T;    scanf("%d",&T);    int n;    while(T-- && ~scanf("%d",&n)){        edge.init();        int u,v;        memset(nofa,-1,sizeof(nofa));        for(int i=1;i<n;i++){            scanf("%d %d",&u,&v);            edge.Link(u,v);            edge.Link(v,u);            nofa[v] = 0;        }        init(n);        scanf("%d %d",&u,&v);        printf("%d\n",lca(u,v));    }    return 0;}