80 points code:

#include<iostream>
using namespace std;
const int N=1e5+5;
int n,head,value[N],nextt[N],id;
void init(){
    head=-1,id=0;
}
void inserthead(int x){
    value[id]=x;
    nextt[id]=head;
    head=id++;
}
void del(int x){
    int flag=0;
    for(int i=head;i!=-1;i=nextt[i]){
        if(value[i]==x){
            flag=i;
            break;
        }
    }
    nextt[flag]=nextt[nextt[flag]];
}
void insert(int x,int y){
    int flag=0;
    for(int i=head;i!=-1;i=nextt[i]){
        if(value[i]==x){
            flag=i;
            break;
        }
    }
    value[id]=y;
    nextt[id]=nextt[flag];
    nextt[flag]=id++;
}
void show(int x){
    int flag=0;
    for(int i=head;i!=-1;i=nextt[i]){
        if(value[i]==x){
            flag=i;
            break;
        }
    }
    if(nextt[flag]==0) cout<<"0"<<endl;
    else cout<<value[nextt[flag]]<<endl;
}
int main(){
    cin>>n;
    init();
    inserthead(1);
    while(n--){
        int t;
        cin>>t;
        if(t==1){
            int x,y;
            cin>>x>>y;
            insert(x,y);
        }
        if(t==2){
            int x;
            cin>>x;
            show(x);
        }
        if(t==3){
            int x;
            cin>>x;
            del(x);
        }
    }
    return 0;
}

优化:利用flag数组标记元素下标 AC code:

#include<iostream>
using namespace std;
const int N=1e6+5;
int n,head,value[N],nextt[N],id,flag[N];
void init(){
    head=-1,id=0;
}
void inserthead(int x){
    value[id]=x;
    nextt[id]=head;
    head=id++;
}
void del(int x){
    int key=flag[x];
    nextt[key]=nextt[nextt[key]];
}
void insert(int x,int y){
    int key=flag[x];
    value[id]=y;
    nextt[id]=nextt[key];
    nextt[key]=id;
    flag[y]=id;
    id++;
}
void show(int x){
    int key=flag[x];
    if(nextt[key]==0) cout<<"0"<<endl;
    else cout<<value[nextt[key]]<<endl;
}
int main(){
    cin>>n;
    init();
    inserthead(1);
    flag[1]=0;
    while(n--){
        int t;
        cin>>t;
        if(t==1){
            int x,y;
            cin>>x>>y;
            insert(x,y);
        }
        if(t==2){
            int x;
            cin>>x;
            show(x);
        }
        if(t==3){
            int x;
            cin>>x;
            del(x);
        }
    }
    return 0;
}