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Create a method to reverse a doubly linked list #2796

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Merged
merged 1 commit into from
Nov 1, 2021
Merged

Create a method to reverse a doubly linked list #2796

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31 changes: 31 additions & 0 deletions DataStructures/Lists/DoublyLinkedList.java
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Original file line number Diff line number Diff line change
Expand Up @@ -218,6 +218,34 @@ public static void removeDuplicates(DoublyLinkedList l) {
}
}

/**
* Reverses the list in place
*
* @param l the DoublyLinkedList to reverse
*/
public void reverse() {
// Keep references to the head and tail
Link thisHead = this.head;
Link thisTail = this.tail;

// Flip the head and tail references
this.head = thisTail;
this.tail = thisHead;

// While the link we're visiting is not null, flip the
// next and previous links
Link nextLink = thisHead;
while (nextLink != null) {
Link nextLinkNext = nextLink.next;
Link nextLinkPrevious = nextLink.previous;
nextLink.next = nextLinkPrevious;
nextLink.previous = nextLinkNext;

// Now, we want to go to the next link
nextLink = nextLinkNext;
}
}

/** Clears List */
public void clearList() {
head = null;
Expand Down Expand Up @@ -299,6 +327,9 @@ public static void main(String args[]) {
myList.display(); // <-- 3(head) <--> 10 <--> 13 <--> 23 <--> 67(tail) -->
myList.insertElementByIndex(5, 1);
myList.display(); // <-- 3(head) <--> 5 <--> 10 <--> 13 <--> 23 <--> 67(tail) -->

myList.reverse(); // <-- 67(head) <--> 23 <--> 13 <--> 10 <--> 5 <--> 3(tail) -->
myList.display();
myList.clearList();
myList.display();
myList.insertHead(20);
Expand Down