binary_lifiting.cpp

#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")

#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp> //required
//#include <ext/pb_ds/tree_policy.hpp> //required

//using namespace __gnu_pbds; //required 
using namespace std;
//template <typename T> using ordered_set =  tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>; 

// ordered_set <int> s;
// s.find_by_order(k); returns the (k+1)th smallest element
// s.order_of_key(k); returns the number of elements in s strictly less than k

#define pb               push_back
#define mp(x,y)          make_pair(x,y)
#define all(x)           x.begin(), x.end()
#define print(vec,l,r)   for(int i = l; i <= r; i++) cout << vec[i] <<" "; cout << endl;
#define input(vec,N)     for(int i = 0; i < (N); i++) cin >> vec[i];
#define debug(...) logger(#__VA_ARGS__, __VA_ARGS__)
#define leftmost_bit(x)  (63-__builtin_clzll(x))
#define rightmost_bit(x) __builtin_ctzll(x) // count trailing zeros
#define set_bits(x)      __builtin_popcountll(x) 
#define pow2(i)          (1LL << (i))
#define is_on(x, i)      ((x) & pow2(i)) // state of the ith bit in x
#define set_on(x, i)     ((x) | pow2(i)) // returns integer x with ith bit on
#define set_off(x, i)    ((x) & ~pow2(i)) // returns integer x with ith bit off
  
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
// auto dist = uniform_int_distribution<int>(l, r);
// use int a = dist(rng) to get a random number between [l,r] inclusive
template<typename ...Args>
void logger(string vars, Args&&... values) {
    cerr << vars << " = ";
    string delim = "";
    (..., (cerr << delim << values, delim = ", "));
	cerr << endl;
}

typedef long long int ll;
typedef long double ld;

const int MOD = 1e9+7; // 998244353;

const ll INF = 1e18; // not too close to LLONG_MAX
const ld PI = acos((ld)-1);
const ld EPS = 1e-8;
const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1}; // for every grid problem!!

// highly risky #defines
#define int ll // disable when you want to make code a bit faster
#define endl '\n' // disable when dealing with interactive problems

typedef vector<int> vi;
typedef pair<int, int> pii;

const int MAXN = 1e5+5;
int n, l; // = 1 + log2(MAXN);
vector<vector<int>> adj;

int timer;
vector<int> height, tin, tout;
vector<vector<int>> up;

void dfs(int v, int p){
    tin[v] = ++timer;
    up[v][0] = p;
    height[v] = 1 + height[p];

    for (int i = 1; i <= l; ++i)
        up[v][i] = up[up[v][i-1]][i-1];

    for (int u : adj[v]) {
        if (u != p)
            dfs(u, v);
    }

    tout[v] = ++timer;
}

bool is_ancestor(int anc, int v){
    return tin[anc] <= tin[v] && tout[anc] >= tout[v];
}

int lca(int u, int v){
    if (is_ancestor(u, v))
        return u;
    if (is_ancestor(v, u))
        return v;
    for (int i = l; i >= 0; --i) {
        if (!is_ancestor(up[u][i], v))
            u = up[u][i];
    }
    return up[u][0];
}

int lca_dist(int anc, int u){
    assert(anc == lca(anc, u));
    if(anc == u) return 0;

    int ans = 1;
    for (int i = l; i >= 0; --i) {
        if (!is_ancestor(up[u][i], anc)){
            u = up[u][i];
            ans += pow2(i);
        }
    }

    return ans;
}

int dist(int u, int v){
    int anc = lca(u, v);
    return lca_dist(anc, u) + lca_dist(anc, v);
}

void preprocess(int root) {
    tin.resize(n);
    tout.resize(n);
    timer = 0;
    l = ceil(log2(n));
    up.assign(n, vector<int>(l + 1));
    height.assign(n, -1);
    dfs(root, root);
}

void solve(){
	// code starts from here
	int q;
    cin >> n >> q;

	adj.clear();
	adj.resize(n);
    height.assign(n, -1);
	for(int u, v, i = 1; i < n; i++){
		cin >> u >> v;
        u--;v--;
        adj[u].pb(v);
        adj[v].pb(u);
	}

	preprocess(0); // usually 0 is root

    for(int t, k, i = 0; i < q; i++){
        cin >> t >> k;
        t--;k--;

        cout << dist(t, k) << endl;
    }
}

signed main(){
 	ios_base::sync_with_stdio(false);
    cin.tie(NULL);

	int T = 1;
	// cin >> T;
	while(T--){
		solve();
	}

	return 0;
}