POJ 3237 Tree
就多一个取负操作，所以线段树结点就把最大和最小值存下来，每次取负的时候，最大和最小值取负后。交换就可以
代码：
#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std; const int N = 10005;
const int INF = 0x3f3f3f3f;
int dep[N], fa[N], son[N], sz[N], top[N], id[N], idx, val[N];
int first[N], next[N * 2], vv[N * 2], en; struct Edge {
int u, v, val;
Edge() {}
Edge(int u, int v, int val) {
this->u = u;
this->v = v;
this->val = val;
}
} e[N]; void init() {
en = 0;
idx = 0;
memset(first, -1, sizeof(first));
} void add_Edge(int u, int v) {
vv[en] = v;
next[en] = first[u];
first[u] = en++;
} void dfs1(int u, int f, int d) {
dep[u] = d;
sz[u] = 1;
fa[u] = f;
son[u] = 0;
for (int i = first[u]; i + 1; i = next[i]) {
int v = vv[i];
if (v == f) continue;
dfs1(v, u, d + 1);
sz[u] += sz[v];
if (sz[son[u]] < sz[v])
son[u] = v;
}
} void dfs2(int u, int tp) {
id[u] = ++idx;
top[u] = tp;
if (son[u]) dfs2(son[u], tp);
for (int i = first[u]; i + 1; i = next[i]) {
int v = vv[i];
if (v == fa[u] || v == son[u]) continue;
dfs2(v, v);
}
} #define lson(x) ((x<<1)+1)
#define rson(x) ((x<<1)+2) struct Node {
int l, r, Max, Min;
bool neg;
} node[N * 4]; void pushup(int x) {
node[x].Max = max(node[lson(x)].Max, node[rson(x)].Max);
node[x].Min = min(node[lson(x)].Min, node[rson(x)].Min);
} void pushdown(int x) {
if (node[x].neg) {
node[lson(x)].Max = -node[lson(x)].Max;
node[rson(x)].Max = -node[rson(x)].Max;
node[lson(x)].Min = -node[lson(x)].Min;
node[rson(x)].Min = -node[rson(x)].Min;
swap(node[lson(x)].Max, node[lson(x)].Min);
swap(node[rson(x)].Max, node[rson(x)].Min);
node[lson(x)].neg = !node[lson(x)].neg;
node[rson(x)].neg = !node[rson(x)].neg;
node[x].neg = false;
}
} void build(int l, int r, int x = 0) {
node[x].l = l; node[x].r = r; node[x].neg = false;
if (l == r) {
node[x].Max = node[x].Min = val[l];
return;
}
int mid = (l + r) / 2;
build(l, mid, lson(x));
build(mid + 1, r, rson(x));
pushup(x);
} void change(int v, int val, int x = 0) {
if (node[x].l == node[x].r) {
node[x].Max = node[x].Min = val;
return;
}
int mid = (node[x].l + node[x].r) / 2;
pushdown(x);
if (v <= mid) change(v, val, lson(x));
if (v > mid) change(v, val, rson(x));
pushup(x);
} void negate(int l, int r, int x = 0) {
if (node[x].l >= l && node[x].r <= r) {
node[x].neg = !node[x].neg;
node[x].Max = -node[x].Max;
node[x].Min = -node[x].Min;
swap(node[x].Max, node[x].Min);
return;
}
int mid = (node[x].l + node[x].r) / 2;
pushdown(x);
if (l <= mid) negate(l, r, lson(x));
if (r > mid) negate(l, r, rson(x));
pushup(x);
} int query(int l, int r, int x = 0) {
if (node[x].l >= l && node[x].r <= r) {
return node[x].Max;
}
int mid = (node[x].l + node[x].r) / 2;
pushdown(x);
int ans = -INF;
if (l <= mid) ans = max(ans, query(l, r, lson(x)));
if (r > mid) ans = max(ans, query(l, r, rson(x)));
pushup(x);
return ans;
} void gao1(int u, int v) {
int tp1 = top[u], tp2 = top[v];
while (tp1 != tp2) {
if (dep[tp1] < dep[tp2]) {
swap(tp1, tp2);
swap(u, v);
}
negate(id[tp1], id[u]);
u = fa[tp1];
tp1 = top[u];
}
if (u == v) return;
if (dep[u] > dep[v]) swap(u, v);
negate(id[son[u]], id[v]);
} int gao2(int u, int v) {
int ans = -INF;
int tp1 = top[u], tp2 = top[v];
while (tp1 != tp2) {
if (dep[tp1] < dep[tp2]) {
swap(tp1, tp2);
swap(u, v);
}
ans = max(ans, query(id[tp1], id[u]));
u = fa[tp1];
tp1 = top[u];
}
if (u == v) return ans;
if (dep[u] > dep[v]) swap(u, v);
ans = max(ans, query(id[son[u]], id[v]));
return ans;
} int T, n; int main() {
scanf("%d", &T);
while (T--) {
init();
scanf("%d", &n);
int u, v, w;
for (int i = 1; i < n; i++) {
scanf("%d%d%d", &u, &v, &w);
add_Edge(u, v);
add_Edge(v, u);
e[i] = Edge(u, v, w);
}
dfs1(1, 0, 1);
dfs2(1, 1);
for (int i = 1; i < n; i++) {
if (dep[e[i].u] < dep[e[i].v]) swap(e[i].u, e[i].v);
val[id[e[i].u]] = e[i].val;
}
build(1, idx);
char Q[10];
int a, b;
while (scanf("%s", Q)) {
if (Q[0] == 'D') break;
scanf("%d%d", &a, &b);
if (Q[0] == 'Q') printf("%d\n", gao2(a, b));
if (Q[0] == 'C') change(id[e[a].u], b);
if (Q[0] == 'N') gao1(a, b);
}
}
return 0;
}