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| #include <cstdio>
#include <algorithm>
#include <vector>
using namespace std;
const int N = 1e5 + 10, M = 2e5 + 10;
int n, m, len, w[N], p[N], d[N], sz[N], rt[N];
int idx, hd[N], nxt[M], edg[M];
int stmp, son[N], dfn[N], top[N];
struct Node
{
int l, r, s;
} tr[2000010];
int _idx;
void pushup(int x)
{
tr[x].s = tr[tr[x].l].s + tr[tr[x].r].s;
}
void modify(int &x, int l, int r, int t)
{
tr[++_idx] = tr[x];
x = _idx;
if (l == r)
{
tr[x].s++;
return;
}
int mid = l + r >> 1;
if (t <= mid)
modify(tr[x].l, l, mid, t);
else
modify(tr[x].r, mid + 1, r, t);
pushup(x);
}
int query(int x1, int x2, int y1, int y2, int l, int r, int k)
{
if (l == r)
return l;
int t = tr[tr[x1].l].s + tr[tr[x2].l].s - tr[tr[y1].l].s - tr[tr[y2].l].s;
int mid = l + r >> 1;
if (t >= k)
return query(tr[x1].l, tr[x2].l, tr[y1].l, tr[y2].l, l, mid, k);
return query(tr[x1].r, tr[x2].r, tr[y1].r, tr[y2].r, mid + 1, r, k - t);
}
void dfs1(int x)
{
sz[x] = 1;
son[x] = -1;
for (int i = hd[x]; ~i; i = nxt[i])
{
if (d[edg[i]])
continue;
d[edg[i]] = d[x] + 1;
p[edg[i]] = x;
dfs1(edg[i]);
sz[x] += sz[edg[i]];
if (son[x] == -1 || sz[edg[i]] > sz[son[x]])
son[x] = edg[i];
}
}
void dfs2(int x, int t)
{
dfn[x] = ++stmp;
top[x] = t;
if (~son[x])
dfs2(son[x], t);
for (int i = hd[x]; ~i; i = nxt[i])
if (edg[i] != son[x] && edg[i] != p[x])
dfs2(edg[i], edg[i]);
}
int LCA(int x, int y)
{
while (top[x] != top[y])
{
if (d[top[x]] < d[top[y]])
swap(x, y);
x = p[top[x]];
}
if (d[x] > d[y])
swap(x, y);
return x;
}
void dfs(int x)
{
rt[x] = rt[p[x]];
modify(rt[x], 1, len, w[x]);
for (int i = hd[x]; ~i; i = nxt[i])
if (edg[i] != p[x])
dfs(edg[i]);
}
void add(int a, int b)
{
nxt[++idx] = hd[a];
hd[a] = idx;
edg[idx] = b;
}
int main()
{
scanf("%d%d", &n, &m);
for (int i = 1; i <= n; i++)
hd[i] = -1;
vector<int> ws;
for (int i = 1; i <= n; i++)
{
scanf("%d", &w[i]);
ws.push_back(w[i]);
}
sort(ws.begin(), ws.end());
len = ws.erase(unique(ws.begin(), ws.end()), ws.end()) - ws.begin();
for (int i = 1; i <= n; i++)
w[i] = lower_bound(ws.begin(), ws.end(), w[i]) - ws.begin() + 1;
for (int i = 1, u, v; i < n; i++)
{
scanf("%d%d", &u, &v);
add(u, v);
add(v, u);
}
d[1] = 1;
dfs1(1);
dfs2(1, 1);
dfs(1);
for (int u, v, k, last = 0; m; m--)
{
scanf("%d%d%d", &u, &v, &k);
u ^= last;
int lca = LCA(u, v);
printf("%d\n", last = ws[query(rt[u], rt[v], rt[lca], rt[p[lca]], 1, len, k) - 1]);
}
return 0;
}
|