add reverse linked list code

Author: ashishps1

patterns/c#/ReverseList.cs

@@ -0,0 +1,23 @@
+public class ListNode {
+    public int val;
+    public ListNode next;
+    public ListNode(int val = 0, ListNode next = null) {
+        this.val = val;
+        this.next = next;
+    }
+}
+
+public class Solution {
+    public ListNode ReverseList(ListNode head) {
+        ListNode prev = null;
+        ListNode curr = head;
+
+        while (curr != null) {
+            ListNode next = curr.next;
+            curr.next = prev;
+            prev = curr;
+            curr = next;
+        }
+        return prev;
+    }
+}

patterns/c++/ReverseList.cpp

@@ -0,0 +1,18 @@
+struct ListNode {
+    int val;
+    ListNode* next;
+    ListNode(int x) : val(x), next(nullptr) {}
+};
+
+ListNode* reverseList(ListNode* head) {
+    ListNode* prev = nullptr;
+    ListNode* curr = head;
+
+    while (curr != nullptr) {
+        ListNode* next = curr->next;
+        curr->next = prev;
+        prev = curr;
+        curr = next;
+    }
+    return prev;
+}

patterns/go/reverse_list.go

@@ -0,0 +1,19 @@
+package main
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func reverseList(head *ListNode) *ListNode {
+	var prev *ListNode = nil
+	curr := head
+
+	for curr != nil {
+		next := curr.Next
+		curr.Next = prev
+		prev = curr
+		curr = next
+	}
+	return prev
+}

patterns/java/ReverseLinkedList.java

@@ -0,0 +1,20 @@
+package patterns.java;
+
+class ListNode {
+    int val;
+    ListNode next;
+}
+
+public class ReverseLinkedList {
+    public ListNode reverseList(ListNode head) {
+        ListNode prev = null; // Previous node, initially null
+        ListNode curr = head; // Current node starts from the head
+        while (curr != null) {
+            ListNode next = curr.next; // Store next node
+            curr.next = prev; // Reverse the current node's pointer
+            prev = curr; // Move prev to current
+            curr = next; // Move curr to next
+        }
+        return prev; // New head of the reversed list
+    }    
+}

patterns/javascript/reverseList.js

@@ -0,0 +1,19 @@
+class ListNode {
+    constructor(val = 0, next = null) {
+        this.val = val;
+        this.next = next;
+    }
+}
+
+function reverseList(head) {
+    let prev = null;
+    let curr = head;
+
+    while (curr !== null) {
+        let next = curr.next;
+        curr.next = prev;
+        prev = curr;
+        curr = next;
+    }
+    return prev;
+}

patterns/python/reverse_list.py

@@ -0,0 +1,16 @@
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+def reverse_list(head):
+    prev = None
+    curr = head
+
+    while curr:
+        next_node = curr.next
+        curr.next = prev
+        prev = curr
+        curr = next_node
+
+    return prev

patterns/typescript/reverseList.ts

@@ -0,0 +1,22 @@
+class ListNode {
+    val: number;
+    next: ListNode | null;
+
+    constructor(val: number = 0, next: ListNode | null = null) {
+        this.val = val;
+        this.next = next;
+    }
+}
+
+function reverseList(head: ListNode | null): ListNode | null {
+    let prev: ListNode | null = null;
+    let curr: ListNode | null = head;
+
+    while (curr !== null) {
+        let next: ListNode | null = curr.next;
+        curr.next = prev;
+        prev = curr;
+        curr = next;
+    }
+    return prev;
+}