func_code_string: #include <bits/stdc++.h>   using namespace std;   const int MAXN = 5e4 + 5;   const int SQRN = 210;   const int BSZ = 256;   vector<int> g[MAXN];   int v[MAXN], lvl[MAXN], pai[MAXN];   int jump[MAXN], best[MAXN][SQRN];   int trie[BSZ * 20 + 5][2];   int n, q, cnt_trie = 1;   void predfs(int cur, int p) {     for (auto viz : g[cur]) {       if (viz == p) continue;       lvl[viz] = lvl[cur] + 1;       pai[viz] = cur;       predfs(viz, cur);     }   }   void build(int cur, int k, int root) {     if (k >= BSZ) return;     jump[root] = cur;     int val = v[cur] ^ k;     int tcur = 1;     for (int i = 16; i >= 0; i--) {       bool viz = val & (1 << i);       if (!trie[tcur][viz]) trie[tcur][viz] = ++cnt_trie;       tcur = trie[tcur][viz];     }     if (pai[cur] == cur) return;     build(pai[cur], k + 1, root);   }   int find_best(int mask) {     int cur = 1;     int resp = 0;     for (int i = 16; i >= 0; i--) {       bool want = 1 ^ ((bool)(mask & (1 << i)));       if (trie[cur][want])         cur = trie[cur][want], resp += (1 << i);       else         cur = trie[cur][!want];     }     return resp;   }   int main() {     scanf( %d %d , &n, &q);     for (int i = 1; i <= n; i++) scanf( %d , &v[i]);     for (int i = 1; i <= n - 1; i++) {       int a, b;       scanf( %d %d , &a, &b);       g[a].push_back(b);       g[b].push_back(a);     }     pai[1] = 1;     predfs(1, 1);     for (int i = 1; i <= n; i++) {       build(i, 0, i);       for (int k = 0; k * BSZ <= n; k++) best[i][k] = find_best(k * BSZ);       memset(trie, 0, sizeof(trie));       cnt_trie = 1;     }     while (q--) {       int a, b;       scanf( %d %d , &a, &b);       int w = 0;       int respf = 0;       while (lvl[jump[b]] > lvl[a]) {         respf = max(respf, best[b][w]);         b = pai[jump[b]];         w++;       }       int dist = w * BSZ;       while (b != a) {         respf = max(respf, v[b] ^ dist);         b = pai[b];         dist++;       }       respf = max(respf, v[a] ^ dist);       printf( %d n , respf);     }   }   