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A singly linked list with reverse…

March 15, 2012, 2:17 am

In (not particularly beautiful) C++, both recursive and non-recursive reverse methods:

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#include <iostream>
using namespace std;
 
class ListItem {
 
public:
 
  ListItem() : next(NULL)
  {}
 
  char data[100];
  ListItem *next;
 
  void reverse(ListItem *p) {
    if(next == NULL) {
      next = p;
    } else {
      next->reverse(this);
      next = p;
    }
  }
};
 
class LinkedList {
 
public:
 
  LinkedList() {}
 
  ListItem *start;
  ListItem *end;
 
  ListItem *push_back(char *data) {
   
 
    ListItem *i = new ListItem();
 
    if(end != NULL) { end->next = i; }
               else { start = i; }
 
    for(size_t n=0;n<100;n++) {i->data[n] = data[n];}
 
    end = i;
    return i;
  }
 
  void reverse() {
    start->reverse(NULL);
    ListItem *temp = end;
    end = start;
    start = temp;
  }
 
  void reverse_nonrec() {
   
    ListItem *last=NULL;
    for(ListItem *p=start;p!=NULL;) {
      ListItem *next = p->next;
 
      p->next = last;
      last = p;
      p = next;
    }
 
    ListItem *temp = end;
    end = start;
    start = temp;
  }
 
  void dump() {
    for(ListItem *p=start;p!=NULL;p=p->next) {
      cout << "data: " << p->data << endl;
    }
  }
 
  ~LinkedList() {
    ListItem *op = NULL;
    for(ListItem *p=start;p!=NULL;p=p->next) {
      if(op != NULL) delete op;
      op = p;
    }
    if(op != NULL) delete op;
  }
 
};
 
int main() {
 
  LinkedList mylist;
 
  char tempdata[100];
  for(size_t n=0;n<100;n++) { tempdata[n] = 'A'; }
  tempdata[99] = 0;
  for(size_t n=0;n<20;n++) {
    mylist.push_back(tempdata);
    for(size_t n=0;n<99;n++) { tempdata[n]++; }
  }
 
  mylist.dump();
  mylist.reverse();
 
  cout << "Reversed List" << endl;
  mylist.dump();
 
  cout << "Reverse again" << endl;
  mylist.reverse_nonrec();
  mylist.dump();
 
   
}
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