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Commit4036244

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add a solution for 148
1 parent06e8e30 commit4036244

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2 files changed

+98
-0
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2 files changed

+98
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‎src/main/java/com/fishercoder/solutions/_148.java

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@@ -140,4 +140,56 @@ int getCount(ListNode head) {
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returncnt;
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}
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}
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publicstaticclassSolution3 {
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/**
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* Credit: https://leetcode.com/problems/sort-list/solution/ top down approach.
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*/
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publicListNodesortList(ListNodehead) {
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if (head ==null ||head.next ==null) {
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returnhead;
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}
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ListNodemid =getMid(head);
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ListNodeleft =sortList(head);
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ListNoderight =sortList(mid);
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returnmergeList(left,right);
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}
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privateListNodemergeList(ListNodeleft,ListNoderight) {
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ListNodepre =newListNode(-1);
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ListNodetmp =pre;
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while (left !=null &&right !=null) {
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if (left.val <right.val) {
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tmp.next =left;
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left =left.next;
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}else {
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tmp.next =right;
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right =right.next;
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}
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tmp =tmp.next;
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}
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if (left !=null) {
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tmp.next =left;
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}elseif (right !=null) {
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tmp.next =right;
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}
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returnpre.next;
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}
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privateListNodegetMid(ListNodehead) {
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/**The key/trick is in this method:
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* it directly uses this head to iterate, so that we could use this top down recursive approach.
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* If we assign head to slow and fast pointers, then this algorithm will run into StackOverflow exception.
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*
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* This is an absolutely amazing method!*/
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ListNodemidPrev =null;
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while (head !=null &&head.next !=null) {
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midPrev = (midPrev ==null) ?head :midPrev.next;
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head =head.next.next;
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}
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ListNodemid =midPrev.next;
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midPrev.next =null;//this is the key, otherwise, StackOverflow exception will occur.
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returnmid;
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}
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}
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}
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packagecom.fishercoder;
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importcom.fishercoder.common.classes.ListNode;
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importcom.fishercoder.common.utils.LinkedListUtils;
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importcom.fishercoder.solutions._148;
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importorg.junit.BeforeClass;
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importorg.junit.Test;
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importstaticorg.junit.Assert.assertEquals;
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publicclass_148Test {
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privatestatic_148.Solution1solution1;
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privatestatic_148.Solution2solution2;
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privatestatic_148.Solution3solution3;
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privatestaticListNodehead;
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privatestaticListNodeexpected;
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@BeforeClass
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publicstaticvoidsetup() {
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solution1 =new_148.Solution1();
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solution2 =new_148.Solution2();
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solution3 =new_148.Solution3();
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}
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@Test
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publicvoidtest1() {
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head =LinkedListUtils.contructLinkedList(newint[]{4,2,1,3});
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expected =LinkedListUtils.contructLinkedList(newint[]{1,2,3,4});
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assertEquals(expected,solution1.sortList(head));
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}
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@Test
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publicvoidtest2() {
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head =LinkedListUtils.contructLinkedList(newint[]{4,2,1,3});
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expected =LinkedListUtils.contructLinkedList(newint[]{1,2,3,4});
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assertEquals(expected,solution2.sortList(head));
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}
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@Test
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publicvoidtest3() {
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head =LinkedListUtils.contructLinkedList(newint[]{4,2,1,3});
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expected =LinkedListUtils.contructLinkedList(newint[]{1,2,3,4});
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assertEquals(expected,solution3.sortList(head));
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}
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}

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