The input contains several test cases.
虽然我没看到这句话但也A了，什么情况。
a到b的路径xor=(a到根xor b到根) 水
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
struct edge {
int t, v;
edge *next;
};
const int maxn = 100009;
const int maxl = 33;
int n, v[maxn], fa[maxn], tr[maxn * maxl][2], tn;
edge *head[maxn], *ep;
inline void addEdge(int u, int v, int w) {
ep-> t = v;
ep-> v = w;
ep-> next = head[u];
head[u] = ep ++;
}
void buildTree() {
static int q[maxn];
int hd = 0, tl = 1;
memset(fa, -1, sizeof(fa));
fa[1] = 0;
q[hd] = 1;
v[1] = 0;
while (hd < tl) {
int p = q[hd ++];
for (edge* e = head[p]; e; e = e-> next)
if (fa[e-> t] == -1) {
fa[e-> t] = p;
v[e-> t] = v[p] ^ e-> v;
q[tl ++] = e-> t;
}
}
}
void trieIns(int v) {
int p = 1;
for (int i = 30; i >= 0; -- i) {
int d = (v >> i) & 1;
if (!tr[p][d])
tr[p][d] = ++ tn;
p = tr[p][d];
}
}
int trieXor(int v) {
int p = 1, s = 0;
for (int i = 30; i >= 0; -- i) {
int d = (v >> i) & 1;
if (tr[p][d ^ 1]) {
s |= (1 << i);
p = tr[p][d ^ 1];
}
else
p = tr[p][d];
}
return s;
}
int main() {
#ifndef ONLINE_JUDGE
freopen("in.txt", "r", stdin);
#endif
scanf("%d", &n);
memset(head, 0, sizeof(head));
ep = new edge[maxn * 2];
for (int i = 0; i < n - 1; ++ i) {
int u, v, w;
scanf("%d%d%d", &u, &v, &w);
addEdge(u, v, w);
addEdge(v, u, w);
}
buildTree();
tr[0][0] = 0;
tr[0][1] = 0;
tr[1][0] = 0;
tr[1][1] = 0;
tn = 2;
for (int i = 1; i <= n; ++ i)
trieIns(v[i]);
int ans = 0;
for (int i = 1; i <= n; ++ i)
ans = max(ans, trieXor(v[i]));
printf("%d\n", ans);
}