create: 0707-design-linked-list.java

java/0707-design-linked-list.java

@@ -0,0 +1,86 @@
+class ListNode {
+    int val;
+    ListNode prev;
+    ListNode next;
+    public ListNode(int val) {
+        this.val = val;
+        this.prev = null;
+        this.next = null;
+    }
+}
+
+class MyLinkedList {
+
+    ListNode left;
+    ListNode right;
+
+    public MyLinkedList() {
+        left = new ListNode(0);
+        right = new ListNode(0);
+        left.next = right;
+        right.prev = left;
+    }
+
+    public int get(int index) {
+        ListNode cur = left.next;
+        while(cur != null && index > 0) {
+            cur = cur.next;
+            index -= 1;
+        }
+        if(cur != null && cur != right && index == 0) {
+            return cur.val;
+        }
+        return -1;
+    }
+
+    public void addAtHead(int val) {
+        ListNode node = new ListNode(val);
+        ListNode next = left.next;
+        ListNode prev = left;
+        prev.next = node;
+        next.prev = node;
+        node.next = next;
+        node.prev = prev;
+    }
+
+    public void addAtTail(int val) {
+        ListNode node = new ListNode(val);
+        ListNode next = right;
+        ListNode prev = right.prev;
+        prev.next = node;
+        next.prev = node;
+        node.next = next;
+        node.prev = prev;
+    }
+
+    public void addAtIndex(int index, int val) {
+        ListNode cur = left.next;
+        while(cur != null && index > 0) {
+            cur = cur.next;
+            index -= 1;
+        }
+        if(cur != null && index == 0) {
+            ListNode node = new ListNode(val);
+            ListNode next = cur;
+            ListNode prev = cur.prev;
+            prev.next = node;
+            next.prev = node;
+            node.next = next;
+            node.prev = prev;
+        }
+    }
+
+    public void deleteAtIndex(int index) {
+        ListNode cur = left.next;
+        while(cur != null && index > 0) {
+            cur = cur.next;
+            index -= 1;
+        }
+        if(cur != null && cur != right && index == 0) {
+            ListNode next = cur.next;
+            ListNode prev = cur.prev;
+            next.prev = prev;
+            prev.next = next;
+        }
+    }
+}