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][20];
int head[maxn];
int tot = 0;
inline void swap_ele(int &a,int &b){
    int c = a;
    a = b;
    b = c;
}
inline int read(){
    int num = 0;
    char c;
    bool flag = false;
    while ((c = getchar()) == ' ' || c == '
' || c == '
');
    if (c == '-')
        flag = true;
    else
        num = c - '0';
    while (isdigit(c = getchar()))
        num = num * 10 + c - '0';
    return (flag ? -1 : 1) * 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!=0;i = edge[i].from){
        int v = edge[i].to;
        if (dep[v] == 0){
            dep[v] = dep[step] + 1;
            f[v][0] = step;
            dfs(v);
        }
    }
}
void init(){

    for (register int i=1;i<=jump_max;i++)
        for (register int j=1;j<=n;j++)
            f[j][i] = f[ f[j][i-1] ][ i-1 ];
}

int lca(int x,int y){
    if (dep[x] < dep[y])
        swap_ele(x,y);
    for (register int i=jump_max;i>=0;--i){
        if (dep[f[x][i]] >= dep[y])
            x = f[x][i];
    }
    if (x == y)
        return y;
    for (register int i=jump_max;i>=0;--i)
        if (f[x][i] != f[y][i]){
            x = f[x][i];
            y = f[y][i];
        }
        
    return f[x][0];
}

int main(){
    n = read();m = read();s = read();
    for (register int i=1;i<=n-1;++i){
        x = read();y = read();
        add_edge(x,y);add_edge(y,x);
    }
    dep[s] = 1;
    dfs(s);
    init();
    for (register int i=1;i<=m;++i){
        a = read();b = read();
        printf("%d
",lca(a,b));
    }
    return 0;
}