Leet code 206 Reverse Linked List (EAZY)

Reverse Linked List :You can solve this problem in C++, Java, Python, or JavaScript using the following algorithm to reverse a singly linked list:

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Imagine you have a chain of beads, and you want to reverse their order. That’s what this code does to a list of numbers. Let’s break it down:

1. We have a list of numbers (like [1, 2, 3, 4, 5]).
2. We start with nothing in our hand (that’s like prev = null) and look at the first number (that’s like current = 1).
3. We take the first number (1) and put it in our other hand. Now our other hand has 1, and the first number (1) is gone.
4. We look at the next number (2) and put it in our other hand. Now our other hand has 2, and the list looks like [1, 3, 4, 5].
5. We keep doing this until there are no more numbers in the list.
6. Finally, our other hand has all the numbers in reverse order (like [5, 4, 3, 2, 1]).

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So, the code takes a list of numbers, starts with an empty hand (prev), and goes through the list, putting the numbers in reverse order in the other hand. When it’s done, it gives you the reversed list.

That’s it! The code helps us reverse a list of numbers just like turning a chain of beads around.

Here’s the code in C++, Java, Python, and JavaScript:

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C++:Leet code 206

class ListNode {
public:
  
ListNode* reverseList(ListNode* head) {
    ListNode* prev = nullptr;
    ListNode* current = head;
    while (current != nullptr) {
        ListNode* next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    return prev; // prev will be the new head of the reversed list
}

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Java: Leet code 206

class ListNode {
  
public ListNode reverseList(ListNode head) {
    ListNode prev = null;
    ListNode current = head;
    while (current != null) {
        ListNode next = current.next;
        current.next = prev;
        prev = current;
        current = next;
    }
    return prev; // prev will be the new head of the reversed list
}

Python: Reverse Linked List

class ListNode:
  def reverseList(head):
    prev = None
    current = head
    while current is not None:
        next_node = current.next
        current.next = prev
        prev = current
        current = next_node
    return prev  # prev will be the new head of the reversed list

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JavaScript: Reverse Linked List

var reverseList = (head) => {
    let prev = null;
    let current = head;
    while (current !== null) {
        const nextNode = current.next;
        current.next = prev;
        prev = current;
        current = nextNode;
    }
    return prev; // prev will be the new head of the reversed list
};

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