RMQ在线求LCA

#include<bits/stdc++.h>using namespace std;#define begin Begin#define next Next#define rank Rank#define REP(i, a, b) for (int i = (a), _end_ = (b); i <= _end_; ++i)#define ER(i, a) for (int i = begin[a]; i; i = next[i])#define debug(...) fprintf(stderr, __VA_ARGS__)template<typename T> inline bool chkmin(T &a, const T &b){ return a > b ? a = b, 1 : 0; }template<typename T> inline bool chkmax(T &a, const T &b){ return a < b ? a = b, 1 : 0; }template<class T> inline T read(){    T sum = 0, fg = 1, c = getchar();    while (c < '0' || c > '9') { if (c == '-') fg = -1; c = getchar(); }    while (c >= '0' && c <= '9') sum = sum * 10 + c - '0', c = getchar();    return sum * fg;}typedef long long LL;const int dmax = 300100, oo = 0x3f3f3f3f;int N, M;int begin[dmax], next[dmax], to[dmax], cnt = 0;void add(const int &x, const int &y, const int &type = 1){    to[++cnt] = y;    next[cnt] = begin[x];    begin[x] = cnt;    if (type) add(y, x, 0);}int lg[dmax];int rank[dmax], dis[dmax], cur = 0, Dis = 0;int rmq[20][dmax];void dfs(const int &x){    rank[x] = ++cur, rmq[0][cur] = x;    ER(i, x)        if (!rank[to[i]])        {            dis[to[i]] = dis[x] + 1, dfs(to[i]);            rmq[0][++cur] = x;        }}inline int Min(const int &x, const int &y) { return dis[x] < dis[y] ? x : y; }inline void log_init() { REP(i, 1, cur) { lg[i] = log(i) / log(2); debug("%d\n", lg[i]); } }inline void rmq_init(){    int N = cur;    REP(i, 1, lg[N])        REP(j, 1, N - (1 << i) + 1)            rmq[i][j] = Min(rmq[i - 1][j], rmq[i - 1][j + (1 << (i - 1))]);}inline int LCA(int x, int y){    x = rank[x], y = rank[y];    if (x > y) swap(x, y);    int k = lg[y - x];    return Min(rmq[k][x], rmq[k][x + (1 << k) + 1]);}inline void init() { dis[1] = 1, dfs(1), log_init(), rmq_init(); }int main(){#ifndef ONLINE_JUDGE    freopen("input.txt", "r", stdin);    freopen("output.txt", "w", stdout);#endif    N = read<int>(), M = read<int>();    REP(i, 1, N - 1) add(read<int>(), read<int>());    init();    while (M--) printf("%d\n", LCA(read<int>(), read<int>()));    return 0;}