141 lines
3.8 KiB
C++
141 lines
3.8 KiB
C++
#include "singly-linked-list.h"
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using namespace seq;
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// return the size (number of items in the singly linked list)
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size_t SinglyLinkedList::size() const
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{
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size_t count = 0;
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for(SinglyLinkedListNode* n = this->head; n != nullptr; n = n->get_next()) count++;
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return count;
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}
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// return pointer to the node at position i, counting from 0
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SinglyLinkedListNode* SinglyLinkedList::index(int i) const
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{
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SinglyLinkedListNode* n = this->head;
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for(int k = 0; k < i; k++)
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{
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assert(n != nullptr);
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n = n->get_next();
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}
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return n;
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}
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// add an item at the end of the list
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void SinglyLinkedList::push_back(const int& pushed_item)
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{
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SinglyLinkedListNode* new_node = new SinglyLinkedListNode;
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new_node->set_item(pushed_item);
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if(this->empty()) this->head = new_node;
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else this->tail->set_next(new_node);
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this->tail = new_node;
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}
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// add an item at the beginning of the list
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void SinglyLinkedList::push_front(const int& pushed_item)
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{
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SinglyLinkedListNode* new_node = new SinglyLinkedListNode;
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new_node->set_item(pushed_item);
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if(this->empty()) this->tail = new_node;
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else new_node->set_next(this->head); // FIG BUG from previous version, which was "else new_node->set_next(this->head->get_next());"
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this->head = new_node;
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}
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// remove the head node and item
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void SinglyLinkedList::pop_front()
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{
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if(this->empty()) return; // nothing there to remove
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SinglyLinkedListNode* successor = this->head->get_next();
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delete this->head;
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this->head = successor; // successor of the previous head is the new head
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if(this->head == nullptr) this->tail = nullptr; // catch special case: the list is now empty
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}
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// remove the tail node and item
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// note: in a singly linked list, we need to walk step by step to the end!
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void SinglyLinkedList::pop_back()
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{
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if(this->empty()) return; // nothing there to remove
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// list only contains one element
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if(this->head->get_next() == nullptr)
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{
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delete this->head;
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this->head = nullptr;
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this->tail = nullptr;
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return;
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}
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/*
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* walk through until "third" is nullptr, second is the last element, and first is the second-to-last
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*/
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SinglyLinkedListNode* first = this->head;
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SinglyLinkedListNode* second = first->get_next();
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SinglyLinkedListNode* third = second->get_next();
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while(third != nullptr)
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{
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first = second;
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second = third;
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third = third->get_next();
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}
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/*
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* remove "second"
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*/
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if(this->tail == second) this->tail = first;
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first->set_next(nullptr);
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delete second;
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}
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// insert an item at index i
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void SinglyLinkedList::insert_at(int i, const int& inserted_item)
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{
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if(i == 0)
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{
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this->push_front(inserted_item);
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return;
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}
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SinglyLinkedListNode* predecessor = this->index(i-1);
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this->insert_successor_to(predecessor, inserted_item);
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}
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// remove the item at index i
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void SinglyLinkedList::erase_at(int i)
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{
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if(i == 0)
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{
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this->pop_front();
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return;
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}
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SinglyLinkedListNode* predecessor = this->index(i-1);
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this->erase_successor_to(predecessor);
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}
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// insert an item after given node
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void SinglyLinkedList::insert_successor_to(SinglyLinkedListNode* predecessor, const int& inserted_item)
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{
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SinglyLinkedListNode* new_node = new SinglyLinkedListNode;
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new_node->set_item(inserted_item);
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SinglyLinkedListNode* successor = predecessor->get_next();
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predecessor->set_next(new_node);
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new_node->set_next(successor);
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if(!successor) this->tail = new_node;
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}
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// remove the item after given node
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void SinglyLinkedList::erase_successor_to(SinglyLinkedListNode* predecessor)
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{
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SinglyLinkedListNode* erased_node = predecessor->get_next();
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SinglyLinkedListNode* new_successor = erased_node->get_next();
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predecessor->set_next(new_successor);
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if(new_successor == nullptr) this->tail = predecessor;
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delete erased_node;
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}
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