2181

Author: lzl124631x

leetcode/2181. Merge Nodes in Between Zeros/README.md

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+# [2181. Merge Nodes in Between Zeros (Medium)](https://leetcode.com/problems/merge-nodes-in-between-zeros/)
+
+<p>You are given the <code>head</code> of a linked list, which contains a series of integers <strong>separated</strong> by <code>0</code>'s. The <strong>beginning</strong> and <strong>end</strong> of the linked list will have <code>Node.val == 0</code>.</p>
+
+<p>For <strong>every </strong>two consecutive <code>0</code>'s, <strong>merge</strong> all the nodes lying in between them into a single node whose value is the <strong>sum</strong> of all the merged nodes. The modified list should not contain any <code>0</code>'s.</p>
+
+<p>Return <em>the</em> <code>head</code> <em>of the modified linked list</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2022/02/02/ex1-1.png" style="width: 600px; height: 41px;">
+<pre><strong>Input:</strong> head = [0,3,1,0,4,5,2,0]
+<strong>Output:</strong> [4,11]
+<strong>Explanation:</strong> 
+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.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2022/02/02/ex2-1.png" style="width: 600px; height: 41px;">
+<pre><strong>Input:</strong> head = [0,1,0,3,0,2,2,0]
+<strong>Output:</strong> [1,3,4]
+<strong>Explanation:</strong> 
+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.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li>The number of nodes in the list is in the range <code>[3, 2 * 10<sup>5</sup>]</code>.</li>
+	<li><code>0 &lt;= Node.val &lt;= 1000</code></li>
+	<li>There are <strong>no</strong> two consecutive nodes with <code>Node.val == 0</code>.</li>
+	<li>The <strong>beginning</strong> and <strong>end</strong> of the linked list have <code>Node.val == 0</code>.</li>
+</ul>
+
+
+**Similar Questions**:
+* [Linked List Components (Medium)](https://leetcode.com/problems/linked-list-components/)
+
+## Solution 1. 
+
+```cpp
+// OJ: https://leetcode.com/problems/merge-nodes-in-between-zeros/
+// Author: github.com/lzl124631x
+// Time: O(N)
+// Space: O(1)
+class Solution {
+public:
+    ListNode* mergeNodes(ListNode* head) {
+        ListNode dummy, *tail = &dummy;
+        while (head) {
+            if (head->val == 0) head = head->next; // skip leading `0`
+            if (!head) break;
+            int sum = 0;
+            while (head->val != 0) { // sum numbers before the next `0`
+                sum += head->val;
+                head = head->next;
+            }
+            tail->next = new ListNode(sum); // append `sum`
+            tail = tail->next;
+        }
+        return dummy.next;
+    }
+};
+```