feat: add linkedList insert method (#774)

Co-authored-by: byj <youjia.bi@weimob.com>

src/data-structures/linked-list/LinkedList.js

@@ -54,6 +54,40 @@ export default class LinkedList {
     return this;
   }
 
+  /**
+   * @param {*} value
+   * @param {*} index
+   * @return {LinkedList}
+   */
+  insert(value, index) {
+    index = index < 0 ? 0 : index;
+    if (index === 0) {
+      this.prepend(value);
+    } else {
+      let count = 1;
+      let currentNode = this.head;
+      const newNode = new LinkedListNode(value);
+      while (currentNode) {
+        if (count === index) break;
+        currentNode = currentNode.next;
+        count++;
+      }
+      if (currentNode) {
+        newNode.next = currentNode.next;
+        currentNode.next = newNode;
+      } else {
+        if (this.tail) {
+          this.tail.next = newNode;
+          this.tail = newNode;
+        } else {
+          this.head = newNode;
+          this.tail = newNode;
+        }
+      }
+    }
+    return this;
+  }
+
   /**
    * @param {*} value
    * @return {LinkedListNode}

src/data-structures/linked-list/__test__/LinkedList.test.js

@@ -32,6 +32,21 @@ describe('LinkedList', () => {
     expect(linkedList.toString()).toBe('3,2,1');
   });
 
+  it('should insert node to linked list', () => {
+    const linkedList = new LinkedList();
+
+    linkedList.insert(4, 3);
+    expect(linkedList.head.toString()).toBe('4');
+    expect(linkedList.tail.toString()).toBe('4');
+
+    linkedList.insert(3, 2);
+    linkedList.insert(2, 1);
+    linkedList.insert(1, -7);
+    linkedList.insert(10, 9);
+
+    expect(linkedList.toString()).toBe('1,4,2,3,10');
+  })
+
   it('should delete node by value from linked list', () => {
     const linkedList = new LinkedList();