SPOJ QTREE(树链剖分)

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 10005;
const int INF = 0x3f3f3f3f;
struct Edge {
int u, v, w, nxt;
Edge() {}
Edge(int a, int b, int c, int d): u(a), v(b), w(c), nxt(d) {}
}e[N << 1];
int size
, son
, fa
, top
, id
, dep
;
int n, head
, cnt, tot, tree[N << 2];

void AddEdge(int u, int v, int w) {
e[cnt] = Edge(u, v, w, head[u]);
head[u] = cnt++;
e[cnt] = Edge(v, u, w, head[v]);
head[v] = cnt++;
}

void dfs2(int u, int tp) {
top[u] = tp;
id[u] = ++tot;
if (son[u]) dfs2(son[u], tp);
for (int i = head[u]; i + 1; i = e[i].nxt) {
int v = e[i].v;
if (v == fa[u] || v == son[u]) continue;
dfs2(v, v);
}
}

void dfs1(int u, int f, int depth) {
size[u] = 1, son[u] = 0, dep[u] = depth, fa[u] = f;
for (int i = head[u]; i + 1; i = e[i].nxt) {
int v = e[i].v;
if (v == f) continue;
dfs1(v, u, depth + 1);
size[u] += size[v];
if (size[son[u]] < size[v]) son[u] = v;
}
}

void pushup(int k) {
tree[k] = max(tree[k * 2], tree[k * 2 + 1]);
}

void modify(int k, int left, int right, int pos, int v) {
if (left == right) {
tree[k] = v;
return;
}
int mid = (left + right) / 2;
if (pos <= mid)
modify(k * 2, left, mid, pos, v);
else
modify(k * 2 + 1, mid + 1, right, pos, v);
pushup(k);
}

int query(int k , int left, int right, int l, int r) {
if (l <= left && right <= r)
return tree[k];
int mid = (left + right) / 2, res = -INF;
if (l <= mid)
res = max(res, query(k * 2, left, mid, l, r));
if (r > mid)
res = max(res, query(k * 2 + 1, mid + 1, right, l, r));
return res;
}

void solve(int u, int v) {
int tp1 = top[u], tp2 = top[v];
int res = -INF;
while (tp1 != tp2) {
if (dep[tp1] < dep[tp2]) {
swap(tp1, tp2);
swap(u, v);
}
res = max(res, query(1, 1, tot, id[tp1], id[u]));
u = fa[tp1];
tp1 = top[u];
}
if (u != v) {
if (dep[u] > dep[v]) swap(u, v);
res = max(res, query(1, 1, tot, id[son[u]], id[v]));
}
printf("%d\n", res);
}

int main() {
int t;
scanf("%d", &t);
while (t--) {
int u, v, w;
memset(head, -1, sizeof(head));
memset(tree, 0, sizeof(tree));
cnt = tot = 0;
scanf("%d", &n);
for (int i = 0; i < n - 1; i++) {
scanf("%d%d%d", &u, &v, &w);
AddEdge(u, v, w);
}
dfs1(1, 0, 1);
dfs2(1, 1);
for (int i = 0; i < cnt; i += 2) {
u = e[i].u, v = e[i].v;
if (dep[u] < dep[v]) swap(u, v);
modify(1, 1, tot, id[u], e[i].w);
}
char op[10];
int a, b;
while (scanf("%s", op) && op[0] != 'D') {
scanf("%d%d", &a, &b);
if (op[0] == 'Q') {
solve(a, b);
}
else {
u = e[a - 1 << 1].u;
v = e[a - 1 << 1].v;
if (dep[u] < dep[v]) swap(u, v);
modify(1, 1, tot, id[u], b);
}
}
if (t) printf("\n");
}
return 0;
}