URAL 1992

可持久化鏈表

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#define N 500010
using namespace std;

int lehead[N],rehead[N];
struct Node{
	int val,next;
}node[N];
int cnt;

void addedge(int u,int val,int * lehead){
	node[cnt].val=val;
	node[cnt].next=lehead[u];
	lehead[u]=cnt++;
}

int main(){
	int n,m,now=1;
	int c,p;
	char s[20];
	scanf("%d %d",&n,&m);
	memset(lehead,-1,sizeof(lehead));
	memset(rehead,-1,sizeof(rehead));
	cnt=0;
	for(int j=1;j<=n;j++){
		scanf("%s",s);
		if(!strcmp(s,"learn")){
			scanf("%d %d",&c,&p);
			addedge(c,p,lehead);
		}
		else if(!strcmp(s,"rollback")){
			scanf("%d",&c);
			addedge(c,node[lehead[c]].val,rehead);
			lehead[c]=node[lehead[c]].next;
		}
		else if(!strcmp(s,"relearn")){
			scanf("%d",&c);
			addedge(c,node[rehead[c]].val,lehead);
			rehead[c]=node[rehead[c]].next;
		}
		else if(!strcmp(s,"clone")){
			scanf("%d",&c);
			now++;
			lehead[now]=lehead[c];
			rehead[now]=rehead[c];
		}
		else{
			scanf("%d",&c);
			if(lehead[c]==-1) printf("basic\n");
			else printf("%d\n",node[lehead[c]].val);
		}
	}
    return 0;
}