CCCPaste

Untitled

#include 
#include 
#include 
#include 
#include 
using namespace std;
const int maxn = 2e5 + 10;
const int logn = 24;
int n;
vector graph[maxn];
int timer = 0;
int in_dfs[maxn], out_dfs[maxn];
int parent[maxn];
int up_node[maxn][logn];
int depth[maxn];
void dfs(int node, int parent, int dist) {
    timer++;
    in_dfs[node] = timer;
    up_node[node][0] = parent;
    depth[node] = dist;
    for(int i = 1; i < logn; i++) {
        up_node[node][i] = up_node[up_node[node][i - 1]][i - 1];
    }
    for(int neighbour : graph[node]) {
        if(neighbour != parent) {
            dfs(neighbour, node, dist + 1);
        }
    }
    timer++;
    out_dfs[node] = timer;
    
}
bool is_ancestor(int A, int B) {
    if(in_dfs[A] <= in_dfs[B] and out_dfs[A] >= out_dfs[B]) {
        return true;
    }
    return false;
}
int LCA(int A, int B) {
    if(is_ancestor(A, B)) {
        return A;
    }
    if(is_ancestor(B, A)) {
        return B;
    }
    for(int i = logn - 1; i >= 0; i--) {
        if(!is_ancestor(up_node[A][i], B)) {
            A = up_node[A][i];
        }
    }
//    cout << A << endl;
    return up_node[A][0];
}
int main() {
    int q;
    cin >> n >> q;
    parent[1] = 0;
    for(int i = 2; i <= n; i++) {
        int a, b;
        cin >> a >> b;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    dfs(1, 1, 0);
    

    for(int i = 0; i < q; i++) {
        int a, b;
        cin >> a >> b;
        int res = depth[a] + depth[b] - 2 * depth[LCA(a, b)];
        cout << res << endl;
    }
    
    return 0;
}

/*
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 **/