feat : merge-two-sorted-lists

Author: ekgns33

merge-two-sorted-lists/ekgns33.java

@@ -0,0 +1,58 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+/**
+ input : two sorted integer linked list
+ output : merged single linked list with sorted order
+ constraints:
+ 1) both linked list can be empty?
+ yes
+ 2) both given lists are sorted?
+ yes
+ edge :
+ 1) if both list are empty return null
+ 2) if one of input lists is empty return the other one
+
+ solution 1)
+ using two pointer
+
+ compare the current pointer's value.
+ get the smaller one, set to the next node
+
+ until both pointer reach the end
+
+ tc : O(n) sc : O(1)
+ */
+class Solution {
+  public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
+    ListNode dummy = new ListNode();
+    ListNode p1 = list1;
+    ListNode p2 = list2;
+    ListNode currNode = dummy;
+    while(p1 != null && p2 != null) {
+      if(p1.val < p2.val){
+        currNode.next = p1;
+        p1 = p1.next;
+      } else {
+        currNode.next = p2;
+        p2 = p2.next;
+      }
+      currNode = currNode.next;
+    }
+
+    if(p1 == null) {
+      currNode.next = p2;
+    } else {
+      currNode.next = p1;
+    }
+
+    return dummy.next;
+  }
+}