Update and rename partition.cpp to partition-list.cpp

Author: kamyu104

C++/partition-list.cpp

@@ -0,0 +1,35 @@
+// Time:  O(n)
+// Space: O(1)
+
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode *partition(ListNode *head, int x) {
+        ListNode dummy_smaller{0};
+        ListNode dummy_larger{0};
+        auto smaller = &dummy_smaller;
+        auto larger = &dummy_larger;
+
+        while (head) {
+            if (head->val < x) {
+                smaller->next = head;
+                smaller = smaller->next;
+            } else {
+                larger->next = head;
+                larger = larger->next;
+            }
+            head = head->next;
+        }
+        smaller->next = dummy_larger.next;
+        larger->next = nullptr;
+
+        return dummy_smaller.next;
+    }
+};