두 리스트 머지

Author: holmir97

MergeTwoLists/ListNode.java

@@ -0,0 +1,18 @@
+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;
+    }
+
+    @Override
+    public String toString() {
+        return val + ",";
+    }
+}

MergeTwoLists/MergeTwoLists.java

@@ -0,0 +1,67 @@
+public class MergeTwoLists {
+    public static void main(String[] args) {
+        ListNode l1 = new ListNode(1, new ListNode(2, new ListNode(4)));
+        ListNode l2 = new ListNode(1, new ListNode(3, new ListNode(4)));
+        System.out.println(new MergeTwoLists().mergeTwoLists(l1, l2));
+    }
+
+
+    //my solution
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        ListNode head = null;
+        ListNode mergeList;
+
+        if (l1 == null && l2 == null)
+            return head;
+        else if (l1 == null || l2 == null) {
+            if (l1 == null)
+                return l2;
+            else
+                return l1;
+        } else {
+            if (l1.val <= l2.val) {
+                mergeList = l1;
+                l1 = l1.next;
+            } else {
+                mergeList = l2;
+                l2 = l2.next;
+            }
+        }head = mergeList;
+
+        while (l1 != null || l2 != null) {
+            if (l1 == null) {
+                mergeList.next = l2;
+                l2 = l2.next;
+            } else if (l2 == null) {
+                mergeList.next = l1;
+                l1 = l1.next;
+            } else if (l1.val <= l2.val) {
+                mergeList.next = l1;
+                l1 = l1.next;
+            } else {
+                mergeList.next = l2;
+                l2 = l2.next;
+            }
+            mergeList = mergeList.next;
+        }
+        return head;
+    }
+}
+
+/* best solution_USE recursive
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        if (l1 == null) {
+            return l2;
+        } else if (l2 == null) {
+            return l1;
+        } else if (l1.val < l2.val) {
+            l1.next = mergeTwoLists(l1.next, l2);
+            return l1;
+        } else {
+            l2.next = mergeTwoLists(l1, l2.next);
+            return l2;
+        }
+    }
+}
+ */