看这篇的链表部分的介绍应该就能理解“可持久化”了

动态分配内存的会T，只能用静态

#include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
           using namespace std;struct node {    int p;    int next;};const int maxn = 500005;node nd[maxn * 2];int ha[maxn], hb[maxn];int c;int cnt;void add(int &head, int p) {    nd[cnt].p = p;    nd[cnt].next = head;    head = cnt++;}int main() {    int n, m;    while(scanf("%d%d", &n, &m) != EOF) {        c = 1;        cnt = 0;        ha[c] = -1; hb[c] = -1;        for(int i = 1; i <= n; i++) {            char op[20]; scanf("%s", op);            if(strcmp(op, "learn") == 0) {                int id, p;                scanf("%d%d", &id, &p);                add(ha[id], p);                hb[id] = -1;            } else if(strcmp(op, "rollback") == 0) {                int id;                scanf("%d", &id);                add(hb[id], nd[ha[id]].p);                ha[id] = nd[ha[id]].next;            } else if(strcmp(op, "clone") == 0) {                int id;                scanf("%d", &id);                c++;                ha[c] = ha[id];                hb[c] = hb[id];            } else if(strcmp(op, "check") == 0) {                int id;                scanf("%d", &id);                if(ha[id] == -1) {                    printf("basic\n");                } else printf("%d\n", nd[ha[id]].p);            } else if(strcmp(op, "relearn") == 0) {                int id;                scanf("%d", &id);                add(ha[id], nd[hb[id]].p);                hb[id] = nd[hb[id]].next;            }        }        return 0;    }    return 0;}