自用lca模板

人丑常数大，总是卡在1000多ms。。。

 #include <cstdio>
 #include <cstring>
 #include <iostream>
 #define maxn 5000005
 #define jump_max 19
 struct Edge{
     int from,to;
 };
 Edge edge[maxn];
 int n,m,s,x,y,a,b;
 int dep[maxn];
 int f[maxn][];
 int head[maxn];
 int tot = ;
 inline void swap_ele(int &a,int &b){
     int c = a;
     a = b;
     b = c;
 }
 inline int read(){
     int num = ;
     char c;
     bool flag = false;
     while ((c = getchar()) == ' ' || c == '\n' || c == '\r');
     if (c == '-')
         flag = true;
     else
         num = c - '';
     while (isdigit(c = getchar()))
         num = num *  + c - '';
     return (flag ? - : ) * num;
 }
 void add_edge(int from,int to){
     edge[++tot].from = head[from];
     edge[tot].to = to;
     head[from] = tot;
 }
 void dfs(int step){
     for (int i=head[step];i!=;i = edge[i].from){
         int v = edge[i].to;
         if (dep[v] == ){
             dep[v] = dep[step] + ;
             f[v][] = step;
             dfs(v);
         }
     }
 }
 void init(){

     for (register int i=;i<=jump_max;i++)
         for (register int j=;j<=n;j++)
             f[j][i] = f[ f[j][i-] ][ i- ];
 }

 int lca(int x,int y){
     if (dep[x] < dep[y])
         swap_ele(x,y);
     for (register int i=jump_max;i>=;--i){
         if (dep[f[x][i]] >= dep[y])
             x = f[x][i];
     }
     if (x == y)
         return y;
     for (register int i=jump_max;i>=;--i)
         if (f[x][i] != f[y][i]){
             x = f[x][i];
             y = f[y][i];
         }

     return f[x][];
 }

 int main(){
     n = read();m = read();s = read();
     for (register int i=;i<=n-;++i){
         x = read();y = read();
         add_edge(x,y);add_edge(y,x);
     }
     dep[s] = ;
     dfs(s);
     init();
     for (register int i=;i<=m;++i){
         a = read();b = read();
         printf("%d\n",lca(a,b));
     }
     return ;
 }