对于修改，将其splay到根再修改。
对于查询x,y路径上的权值和，先将x换到根，再access(y)、splay(y)，sum[y]就是答案。
代码：
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 using namespace std; 5 inline char nc(){ 6 static char buf[100000],*p1=buf,*p2=buf; 7 if(p1==p2){ 8 p2=(p1=buf)+fread(buf,1,100000,stdin); 9 if(p1==p2)return EOF; 10 } 11 return *p1++; 12 } 13 inline void Read(int& x){ 14 char c=nc(); 15 for(;c<'0'||c>'9';c=nc()); 16 for(x=0;c>='0'&&c<='9';x=(x<<3)+(x<<1)+c-48,c=nc()); 17 } 18 inline void Read(char &C){ 19 char c=nc(); 20 while(c<'a'||c>'z')c=nc(); 21 C=c; 22 } 23 char S[30]; 24 int Len; 25 inline void Print(int x){ 26 if(x==0)putchar(48); 27 for(Len=0;x;x/=10)S[++Len]=x%10; 28 for(;Len;)putchar(S[Len--]+48);putchar(' '); 29 } 30 #define N 30010 31 int i,j,k,n,x,y,m,f[N],ch[N][2],a[N],s[N]; 32 bool b[N],r[N]; 33 char c; 34 inline int Get(int x){return ch[f[x]][1]==x;} 35 inline void Update(int x){ 36 if(x==0)return; 37 r[x]^=1; 38 swap(ch[x][0],ch[x][1]); 39 } 40 inline void Pushdown(int x){if(r[x])Update(ch[x][0]),Update(ch[x][1]),r[x]=0;} 41 inline void Pushup(int x){s[x]=s[ch[x][0]]+s[ch[x][1]]+a[x];} 42 inline void Rotate(int x){ 43 bool d=Get(x);int y=f[x]; 44 if(b[y])b[y]=0,b[x]=1;else ch[f[y]][Get(y)]=x; 45 ch[y][d]=ch[x][d^1];f[ch[y][d]]=y; 46 ch[x][d^1]=y;f[x]=f[y];f[y]=x; 47 Pushup(y); 48 } 49 inline void P(int x){ 50 if(!b[x])P(f[x]); 51 Pushdown(x); 52 } 53 inline void Splay(int x){ 54 P(x); 55 for(;!b[x];Rotate(x)) 56 if(!b[f[x]])Rotate(Get(x)==Get(f[x])?f[x]:x); 57 Pushup(x); 58 } 59 inline int Access(int x){ 60 int y=0; 61 while(x){ 62 Splay(x); 63 b[ch[x][1]]=1;ch[x][1]=y;b[y]=0; 64 Pushup(x);y=x;x=f[x]; 65 } 66 return y; 67 } 68 inline bool Judge(int x,int y){ 69 while(f[x])x=f[x]; 70 while(f[y])y=f[y]; 71 return x==y; 72 } 73 inline void mr(int x){Access(x);Splay(x);Update(x);} 74 inline void Link(int x,int y){mr(x);f[x]=y;} 75 inline void Change(int x,int y){Splay(x);s[x]+=y-a[x];a[x]=y;} 76 inline int Query(int x,int y){ 77 if(x==y)return a[x]; 78 mr(x);Access(y);Splay(y);return s[y]; 79 } 80 int main() 81 { 82 Read(n); 83 for(i=1;i<=n;i++)Read(a[i]),s[i]=a[i],b[i]=1; 84 Read(m); 85 while(m--){ 86 Read(c);Read(x);Read(y); 87 if(c=='e')if(!Judge(x,y))puts("impossible");else Print(Query(x,y));else 88 if(c=='b')if(Judge(x,y))puts("no");else puts("yes"),Link(x,y);else Change(x,y); 89 } 90 return 0; 91 }