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| #include <bits/stdc++.h>
#define R register
#define ll long long
#define sum(a, b, mod) (((a) + (b)) % mod)
const int MaxN = 2e5 + 10;
struct edge
{
int next, to;
};
struct node
{
int l, r;
int min, sec, tag;
};
edge e[MaxN << 1];
int n, m, cnt, dfscnt;
int head[MaxN], fa[MaxN], dep[MaxN], dfn[MaxN], pre[MaxN], size[MaxN];
struct SegmentTree
{
node t[MaxN << 2];
void pushup(int id)
{
int lc = id << 1, rc = id << 1 | 1;
if(t[lc].min == t[rc].min)
{
t[id].min = t[lc].min;
t[id].sec = std::min(t[lc].sec, t[rc].sec);
}
else if(t[lc].min < t[rc].min)
{
t[id].min = t[lc].min;
t[id].sec = std::min(t[lc].sec, t[rc].min);
}
else
{
t[id].min = t[rc].min;
t[id].sec = std::min(t[lc].min, t[rc].sec);
}
}
void build(int id, int l, int r)
{
t[id].l = l, t[id].r = r, t[id].tag = -1;
if(l == r) return (void) (t[id].min = 1, t[id].sec = 0x3f3f3f3f);
int mid = (l + r) >> 1;
build(id << 1, l, mid), build(id << 1 | 1, mid + 1, r);
}
void pushtag(int id, int val)
{
if(t[id].min >= val) return;
t[id].min = t[id].tag = val;
}
void pushdown(int id)
{
if(t[id].tag == -1) return;
pushtag(id << 1, t[id].tag), pushtag(id << 1 | 1, t[id].tag);
t[id].tag = -1;
}
void setval(int id, int l, int r, int val)
{
if(t[id].min >= val) return;
if(t[id].l > r || l > t[id].r) return;
if(l <= t[id].l && t[id].r <= r && t[id].sec > val)
return pushtag(id, val);
pushdown(id), setval(id << 1, l, r, val);
setval(id << 1 | 1, l, r, val), pushup(id);
}
int query(int id, int pos)
{
if(t[id].l > pos || t[id].r < pos)
return 0x3f3f3f3f;
if(t[id].l == t[id].r) return t[id].min;
pushdown(id);
return std::min(query(id << 1, pos), query(id << 1 | 1, pos));
}
}T;
void add_edge(int u, int v)
{
++cnt;
e[cnt].to = v;
e[cnt].next = head[u];
head[u] = cnt;
}
void dfs(int u, int fa)
{
dep[u] = dep[fa] + 1, ::fa[u] = fa;
dfn[u] = ++dfscnt, pre[dfscnt] = u, size[u] = 1;
for(int i = head[u]; i; i = e[i].next)
{
int v = e[i].to;
if(v == fa) continue;
dfs(v, u), size[u] += size[v];
}
}
char get()
{
char ch = getchar();
while(!isalpha(ch))
ch = getchar();
return ch;
}
inline int read()
{
int x = 0;
char ch = getchar();
while(ch > '9' || ch < '0')
ch = getchar();
while(ch <= '9' && ch >= '0')
x = (x << 1) + (x << 3) + (ch ^ 48), ch = getchar();
return x;
}
int main()
{
n = read(), m = read();
for(int i = 1; i < n; i++)
{
int u = read(), v = read();
add_edge(u, v), add_edge(v, u);
}
dfs(1, 0), T.build(1, 1, n);
while(m--)
{
char op = get();
int u = read();
if(op == 'Q')
printf("%d\n", pre[T.query(1, dfn[u])]);
else T.setval(1, dfn[u], dfn[u] + size[u] - 1, dfn[u]);
}
return 0;
}
|