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| #include <bits/stdc++.h>
#define x first
#define y second
#define y1 Y1
#define y2 Y2
#define mp make_pair
#define pb push_back
using namespace std;
typedef long long LL;
typedef pair <int, int> pii;
template <typename T> inline int Chkmax (T &a, T b) { return a < b ? a = b, 1 : 0; }
template <typename T> inline int Chkmin (T &a, T b) { return a > b ? a = b, 1 : 0; }
template <typename T> inline T read ()
{
T sum = 0, fl = 1; char ch = getchar();
for (; !isdigit(ch); ch = getchar()) if (ch == '-') fl = -1;
for (; isdigit(ch); ch = getchar()) sum = (sum << 3) + (sum << 1) + ch - '0';
return sum * fl;
}
inline void proc_status ()
{
ifstream t ("/proc/self/status");
cerr << string (istreambuf_iterator <char> (t), istreambuf_iterator <char> ()) << endl;
}
const int Maxn = 2e4 + 100, Maxlen = 60;
int N, Q;
int e, Begin[Maxn], To[Maxn << 1], Next[Maxn << 1];
LL W[Maxn];
struct Basis
{
LL A[Maxlen + 1];
inline void init () { memset(A, 0, sizeof A); }
inline int insert (LL x)
{
for (int i = Maxlen; i >= 0; --i)
{
if (!(x & (1ll << i))) continue;
if (!A[i])
{
for (int j = 0; j < i; ++j) if (x & (1ll << j)) x ^= A[j];
for (int j = i + 1; j <= Maxlen; ++j) if (A[j] & (1ll << i)) A[j] ^= x;
A[i] = x;
return 1;
}
x ^= A[i];
}
return 0;
}
friend Basis merge (const Basis &a, const Basis &b)
{
Basis ans = a;
for (int i = 0; i <= Maxlen; ++i) if (b.A[i]) ans.insert (b.A[i]);
return ans;
}
inline LL query (LL ans = 0)
{
for (int i = 0; i <= Maxlen; ++i) Chkmax(ans, ans ^ A[i]);
return ans;
}
} B[15 + 1][Maxn];
inline void add_edge (int x, int y) { To[++e] = y; Next[e] = Begin[x]; Begin[x] = e; }
int anc[15 + 1][Maxn], dep[Maxn];
inline void dfs (int x)
{
dep[x] = dep[anc[0][x]] + 1;
B[0][x].insert (W[x]);
for (int i = 1; i <= 15; ++i)
{
anc[i][x] = anc[i - 1][anc[i - 1][x]];
B[i][x] = merge (B[i - 1][x], B[i - 1][anc[i - 1][x]]);
}
for (int i = Begin[x]; i; i = Next[i])
{
int y = To[i]; if (y == anc[0][x]) continue;
anc[0][y] = x;
dfs(y);
}
}
Basis ans;
inline void get_lca (int x, int y)
{
ans.insert(W[x]), ans.insert(W[y]);
if (dep[x] < dep[y]) swap(x, y);
for (int i = 15; i >= 0; --i)
if (dep[anc[i][x]] >= dep[y])
{
ans = merge (ans, B[i][x]);
x = anc[i][x];
}
if (x == y) return ;
for (int i = 15; i >= 0; --i)
if (anc[i][x] != anc[i][y])
{
ans = merge(ans, merge(B[i][x], B[i][y]));
x = anc[i][x], y = anc[i][y];
}
ans.insert(W[x]), ans.insert(W[y]);
ans.insert(W[anc[0][x]]);
}
inline void Solve ()
{
dfs(1);
while (Q--)
{
int x = read<int>(), y = read<int>();
ans.init();
get_lca (x, y);
printf("%lld\n", ans.query());
}
}
inline void Input ()
{
N = read<int>(), Q = read<int>();
for (int i = 1; i <= N; ++i) W[i] = read<LL>();
for (int i = 1; i < N; ++i)
{
int x = read<int>(), y = read<int>();
add_edge (x, y);
add_edge (y, x);
}
}
int main()
{
#ifndef ONLINE_JUDGE
freopen("A.in", "r", stdin);
freopen("A.out", "w", stdout);
#endif
Input();
Solve();
return 0;
}
|