Luogu2420 让我们异或吧 （熟练剖分）

\(dis[u] \bigoplus dis[v] = dis[u] \bigoplus dis[v] \bigoplus dis[lca\{x,y\}] \bigoplus dis[lca\{x,y\}]\)

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int  a = (b); a <= (c); ++ a)
#define nR(a,b,c) for(register int  a = (b); a >= (c); -- a)
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Abs(a) ((a) < 0 ? -(a) : (a))
#define Swap(a,b) a^=b^=a^=b
#define ll long long

#define ON_DEBUG

#ifdef ON_DEBUG

#define D_e_Line printf("\n\n----------\n\n")
#define D_e(x)  cout << #x << " = " << x << endl
#define Pause() system("pause")
#define FileOpen() freopen("in.txt","r",stdin);

#else

#define D_e_Line ;
#define D_e(x)  ;
#define Pause() ;
#define FileOpen() ;

#endif

struct ios{
    template<typename ATP>ios& operator >> (ATP &x){
        x = 0; int f = 1; char c;
        for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-')  f = -1;
        while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();
        x*= f;
        return *this;
    }
}io;
using namespace std;

const int N = 100007;

int n;

struct Edge{
	int nxt, pre, w;
}e[N << 1];
int head[N], cntEdge;
inline void add(int u, int v, int w){
	e[++cntEdge] = (Edge){head[u], v, w}, head[u] = cntEdge;
}

int siz[N], dis[N], fa[N], son[N], dep[N];
inline void DFS_First(int u, int father){
	siz[u] = 1, fa[u] = father, dep[u] = dep[father] + 1;
	for(register int i = head[u]; i; i = e[i].nxt){
		int v = e[i].pre;
		if(v == father) continue;
		dis[v] = dis[u] ^ e[i].w;
		DFS_First(v, u);
		siz[u] += siz[v];
		if(!son[u] || siz[v] > siz[son[u]]){
			son[u] = v;
		}
	}
}
int dfn[N], dfnIndex, top[N];
inline void DFS_Second(int u, int ancester){
	top[u] = ancester, dfn[u] = ++dfnIndex;
	if(!son[u]) return;
	DFS_Second(son[u], ancester);
	for(register int i = head[u]; i; i = e[i].nxt){
		int v = e[i].pre;
		if(v != son[u] && v != fa[u]){
			DFS_Second(v,v);
		}
	}
}
inline int LCA(int x, int y){
	while(top[x] != top[y]){
		if(dep[top[x]] < dep[top[y]]) Swap(x, y);
		x = fa[top[x]];
	}
	return dep[x] < dep[y] ? x : y;
}

int main(){
	io >> n;
	R(i,2,n){
		int u, v, w;
		io >> u >> v >> w;
		add(u, v, w);
		add(v, u, w);
	}
	
	DFS_First(1, 0);
	DFS_Second(1, 1);
	
	int m;
	io >> m;
	while(m--){
		int l, r;
		io >> l >> r;
		int lca = LCA(l, r);
		printf("%d\n", dis[l] ^ dis[r] ^ dis[lca] ^ dis[lca]);
	}
	
	return 0;
}