feat: add No.2181

Author: BaffinLee

2101-2200/2181. Merge Nodes in Between Zeros.md

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+# 2181. Merge Nodes in Between Zeros
+
+- Difficulty: Medium.
+- Related Topics: Linked List, Simulation.
+- Similar Questions: Linked List Components.
+
+## Problem
+
+You are given the `head` of a linked list, which contains a series of integers **separated** by `0`'s. The **beginning** and **end** of the linked list will have `Node.val == 0`.
+
+For **every **two consecutive `0`'s, **merge** all the nodes lying in between them into a single node whose value is the **sum** of all the merged nodes. The modified list should not contain any `0`'s.
+
+Return **the** `head` **of the modified linked list**.
+
+ 
+Example 1:
+
+![](https://assets.leetcode.com/uploads/2022/02/02/ex1-1.png)
+
+```
+Input: head = [0,3,1,0,4,5,2,0]
+Output: [4,11]
+Explanation: 
+The above figure represents the given linked list. The modified list contains
+- The sum of the nodes marked in green: 3 + 1 = 4.
+- The sum of the nodes marked in red: 4 + 5 + 2 = 11.
+```
+
+Example 2:
+
+![](https://assets.leetcode.com/uploads/2022/02/02/ex2-1.png)
+
+```
+Input: head = [0,1,0,3,0,2,2,0]
+Output: [1,3,4]
+Explanation: 
+The above figure represents the given linked list. The modified list contains
+- The sum of the nodes marked in green: 1 = 1.
+- The sum of the nodes marked in red: 3 = 3.
+- The sum of the nodes marked in yellow: 2 + 2 = 4.
+```
+
+ 
+**Constraints:**
+
+
+	
+- The number of nodes in the list is in the range `[3, 2 * 105]`.
+	
+- `0 <= Node.val <= 1000`
+	
+- There are **no** two consecutive nodes with `Node.val == 0`.
+	
+- The **beginning** and **end** of the linked list have `Node.val == 0`.
+
+
+
+## Solution
+
+```javascript
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+var mergeNodes = function(head) {
+    var newHead = new ListNode();
+    var resNow = newHead;
+    var now = head;
+    while (now) {
+        if (now.val === 0 && now.next) {
+            resNow.next = new ListNode();
+            resNow = resNow.next;
+        } else if (now.val !== 0) {
+            resNow.val += now.val;
+        }
+        now = now.next;
+    }
+    return newHead.next;
+};
+```
+
+**Explain:**
+
+nope.
+
+**Complexity:**
+
+* Time complexity : O(n).
+* Space complexity : O(n).