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| #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn = 20005;
struct edge {
int to, nxt;
}e[maxn << 1];
int n, q, lnk[maxn], ptr;
int dfn[maxn], cnt, top[maxn], f[maxn];
int dep[maxn], siz[maxn], mxson[maxn];
ll a[maxn], w[maxn];
struct LB {
ll v[61];
ll& operator[](int x) {
return v[x];
}
}s[maxn << 2], ans;
inline int rd() {
register int x = 0, c = getchar();
while (!isdigit(c)) c = getchar();
while (isdigit(c)) x = x * 10 + (c ^ 48), c = getchar();
return x;
}
inline ll rdll() {
register ll x = 0; register int c = getchar();
while (!isdigit(c)) c = getchar();
while (isdigit(c)) x = x * 10 + (c ^ 48), c = getchar();
return x;
}
inline void add(int bgn, int end) {
e[++ptr] = (edge){end, lnk[bgn]};
lnk[bgn] = ptr;
}
void dfs1(int x, int fa) {
dep[x] = dep[fa] + 1;
siz[x] = 1;
f[x] = fa;
for (int p = lnk[x]; p; p = e[p].nxt) {
int y = e[p].to;
if (y == fa) continue;
dfs1(y, x);
siz[x] += siz[y];
if (siz[y] > siz[mxson[x]]) mxson[x] = y;
}
}
void dfs2(int x, int init) {
top[x] = init;
dfn[x] = ++cnt;
w[cnt] = a[x];
if (!mxson[x]) return;
dfs2(mxson[x], init);
for (int p = lnk[x]; p; p = e[p].nxt) {
int y = e[p].to;
if (y == mxson[x] || y == f[x]) continue;
dfs2(y, y);
}
}
void merge(LB &res, LB &l, LB &r) {
LB ret;
for (int i = 60; ~i; --i) ret[i] = l[i];
for (int i = 60; ~i; --i)
if (r[i]) {
ll p = r[i];
for (int i = 60; ~i; --i)
if (p & (1ll << i)) {
if (!ret[i]) {
ret[i] = p; break;
} else p ^= ret[i];
}
}
for (int i = 60; ~i; --i)
res[i] = ret[i];
}
void build(int cur, int l, int r) {
if (l == r) {
ll p = w[l];
for (int i = 60; ~i; --i)
if (p & (1ll << i)) {
if (!s[cur][i]) {
s[cur][i] = p; break;
} else p ^= s[cur][i];
}
return;
}
int mid = (l + r) >> 1;
build(cur << 1, l, mid);
build(cur << 1|1, mid + 1, r);
merge(s[cur], s[cur << 1], s[cur << 1|1]);
}
void query(int cur, int l, int r, int L, int R) {
if (L <= l && r <= R) {
merge(ans, ans, s[cur]);
return;
}
int mid = (l + r) >> 1;
if (L <= mid) query(cur << 1, l, mid, L, R);
if (R > mid) query(cur << 1|1, mid + 1, r, L, R);
}
void queryt(int x, int y) {
memset(ans.v, 0, sizeof ans.v);
while (top[x] != top[y]) {
if (dep[top[x]] < dep[top[y]]) swap(x, y);
query(1, 1, n, dfn[top[x]], dfn[x]);
x = f[top[x]];
}
if (dep[x] > dep[y]) swap(x, y);
query(1, 1, n, dfn[x], dfn[y]);
}
int main() {
n = rd(); q = rd();
for (int i = 1; i <= n; ++i)
a[i] = rdll();
int u, v;
for (int i = 1; i < n; ++i) {
u = rd(); v = rd();
add(u, v); add(v, u);
}
dfs1(1, 0);
dfs2(1, 1);
build(1, 1, n);
while (q--) {
u = rd(); v = rd();
queryt(u, v);
ll res = 0;
for (int i = 60; ~i; --i) {
if ((res ^ ans[i]) > res)
res ^= ans[i];
}
printf("%lld\n", res);
}
return 0;
}
|
