LCA

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#include <cstdio>#include <algorithm>using namespace std;const int N = 100010;const int M = N + N;const int P = 16;int n, q;int head[N], dest[M], last[M], etot;int dep[N], anc[N][P+1];void adde( int u, int v ) {    etot++;    dest[etot] = v;    last[etot] = head[u];    head[u] = etot;}void dfs( int u, int f ) {    anc[u][0] = f;    for( int p = 1; p <= P; p++ )         anc[u][p] = anc[anc[u][p-1]][p-1];    for( int t = head[u]; t; t = last[t] ) {        int v = dest[t];        if( v == f ) continue;        dep[v] = dep[u] + 1;        dfs( v, u );    }}int lca( int u, int v ) {    if( dep[u] < dep[v] ) swap(u,v);    int t = dep[u] - dep[v];    /*    for( int p = 0; p <= P; p++ )        if( t & (1<<p) ) u = anc[u][p];    */    for( int p = 0; p <= P; p++ )        if( t & (1<<p) ) u = anc[u][p];    for( int p = 0; t; t >>= 1, p++ )        if( t & 1 ) u = anc[u][p];    if( u == v ) return u;    for( int p = P; p >= 0 /*anc[u][0] != anc[v][0]*/; p-- )         if( anc[u][p] != anc[v][p] )            u = anc[u][p], v = anc[v][p];    return anc[u][0];}int main() {    scanf( "%d", &n );    for( int i = 1; i < n; i++ ) {        int u, v;        scanf( "%d%d", &u, &v );        adde( u, v );        adde( v, u );    }    dep[1] = 1;    dfs( 1, 1 );    scanf( "%d", &q );    while( q-- ) {        int u, v;        scanf( "%d%d", &u, &v );        printf( "%d\n", lca(u,v) );    }}
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