Merge pull request #2447 from rzvl/design-linked-list-js

Add 0707-design-linked-list.js

Author: Ykhan799

javascript/0707-design-linked-list.js

@@ -0,0 +1,89 @@
+class Node {
+    constructor(val) {
+        this.val = val;
+        this.prev = null;
+        this.next = null;
+    }
+}
+
+class MyLinkedList {
+    constructor() {
+        this.head = null;
+        this.tail = null;
+    }
+
+    get(index) {
+        let curr = this.head;
+        while (curr && index > 0) {
+            curr = curr.next;
+            index--;
+        }
+        return curr ? curr.val : -1;
+    }
+
+    addAtHead(val) {
+        if (this.head === null) {
+            this.head = new Node(val);
+            this.tail = this.head;
+        } else {
+            this.head.prev = new Node(val);
+            this.head.prev.next = this.head;
+            this.head = this.head.prev;
+        }
+    }
+
+    addAtTail(val) {
+        if (this.head === null) {
+            this.head = new Node(val);
+            this.tail = this.head;
+        } else {
+            this.tail.next = new Node(val);
+            this.tail.next.prev = this.tail;
+            this.tail = this.tail.next;
+        }
+    }
+
+    addAtIndex(index, val) {
+        if (index === 0) this.addAtHead(val);
+        else {
+            let curr = this.head;
+            while (curr && index > 0) {
+                curr = curr.next;
+                index--;
+            }
+            if (index === 0) {
+                if (!curr) this.addAtTail(val);
+                else {
+                    const prev = curr.prev;
+                    prev.next = new Node(val);
+                    prev.next.prev = prev;
+                    prev.next.next = curr;
+                    curr.prev = prev.next;
+                }
+            }
+        }
+    }
+
+    deleteAtIndex(index) {
+        if (!this.head) return;
+        if (index === 0) {
+            this.head = this.head.next;
+            if (this.head) this.head.prev = null;
+        } else {
+            let curr = this.head;
+            while (curr && index > 0) {
+                curr = curr.next;
+                index--;
+            }
+            if (curr && index === 0) {
+                if (!curr.next) {
+                    curr.prev.next = null;
+                    this.tail = curr.prev;
+                } else {
+                    curr.prev.next = curr.next;
+                    curr.next.prev = curr.prev;
+                }
+            }
+        }
+    }
+}