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Commit 5d5f2b8

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LC#21 merge two sorted linkedlists, 2 approaches, recursive and iterative
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package LinkedList;
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public class MergeTwoSortedLists21 {
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public class ListNode {
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int val;
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ListNode next;
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ListNode() {
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}
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ListNode(int val) {
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this.val = val;
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}
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ListNode(int val, ListNode next) {
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this.val = val;
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this.next = next;
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}
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}
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// recursive
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public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
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return merge(list1, list2);
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}
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private ListNode merge(ListNode list1, ListNode list2) {
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if (list1 == null)
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return list2;
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if (list2 == null)
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return list1;
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if (list1.val < list2.val) {
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list1.next = merge(list1.next, list2);
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return list1;
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} else {
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list2.next = merge(list1, list2.next);
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return list2;
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}
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}
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// iterative
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public ListNode mergeTwoListsIterative(ListNode list1, ListNode list2) {
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if (list1 == null)
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return list2;
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if (list2 == null)
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return list1;
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ListNode mergedAns;
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ListNode tail;
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if (list1.val < list2.val) {
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mergedAns = list1;
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tail = list1;
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list1 = list1.next;
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} else {
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mergedAns = list2;
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tail = list2;
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list2 = list2.next;
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}
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while (list1 != null && list2 != null) {
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if (list1.val < list2.val) {
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tail.next = list1;
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tail = list1;
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list1 = list1.next;
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} else {
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tail.next = list2;
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tail = list2;
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list2 = list2.next;
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}
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}
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if (list1 == null)
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tail.next = list2;
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if (list2 == null)
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tail.next = list1;
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return mergedAns;
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}
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}

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