Merge Two Sorted Lists & Remove Nth Node From End of List

1.合并兩個排好序的list

Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

2.删除list倒數第n個元素

Remove Nth Node From End of List

Given a linked list, remove the nth node from the end of list and return its head.

For example,

Given linked list: 1->2->3->4->5, and n = 2.

   After removing the second node from the end, the linked list becomes 1->2->3->5.
      

Note:

Given n will always be valid.

Try to do this in one pass.

兩個問題合在一個工程裡面測試

1 package com.rust.datastruct;
  2 
  3 public class MergeTwoSortedLists {
  4     public static ListNode mergeTwoSortedLists(ListNode l1, ListNode l2) {
  5         ListNode r1 = new ListNode(0);
  6         ListNode res = r1;
  7         ListNode t1 = l1;//java 中這樣的指派操作，對了l1操作等同于對t1操作
  8         ListNode t2 = l2;
  9         while (t1 != null && t2 != null){
 10             if (t1.val <= t2.val) {
 11                 r1.next = t1;
 12                 t1 = t1.next;
 13             } else {
 14                 r1.next = t2;
 15                 t2 = t2.next;
 16             }
 17             r1 = r1.next;
 18         }
 19         if (t1 != null) {
 20             r1.next = t1;
 21         }
 22         if (t2 != null) {
 23             r1.next = t2;
 24         }
 25         res = res.next;
 26         return res;
 27     }
 28     /**
 29      * @param head
 30      * @param n
 31      * @return ListNode
 32      */
 33     public static ListNode removeNthFromEnd(ListNode head, int n) {
 34         if (n == 0) return head;
 35         ListNode fakeNode = head;
 36         int count = 0;
 37         while (fakeNode != null) {
 38             fakeNode = fakeNode.next;
 39             count++;
 40         }
 41         fakeNode = head;
 42         if (n == count) {
 43             head = head.next;
 44             return head;
 45         } else {
 46             for (int i = 0; i < count; i++) {
 47                 if (i + n + 1== count) {
 48                     System.out.println(fakeNode.val);
 49                     ListNode cut = fakeNode.next.next;
 50                     fakeNode.next = cut;
 51                     count--;
 52                     continue;
 53                 }
 54                 fakeNode = fakeNode.next;
 55             }
 56         }
 57         return head;
 58     }
 59     
 60     public static void main(String args[]){
 61         ListNode l1 = new ListNode(0);
 62         ListNode l2 = new ListNode(1);
 63         ListNode p1 = l1;
 64         ListNode p2 = l2;
 65         /*initial the list*/
 66         for (int i = 2; i <= 10; i++) {
 67             if (i%2 == 0) {
 68                 p1.next = new ListNode(i);
 69                 p1 = p1.next;
 70             } else {
 71                 p2.next = new ListNode(i);
 72                 p2 = p2.next;
 73             }
 74         }
 75         p1 = l1;
 76         p2 = l2;
 77         System.out.println("input List l1 and l2");
 78         showData(l1, l2);//after show,l1 and l2 value didn't change!
 79         System.out.println("mergeTwoLists(l1, l2) -->");
 80         ListNode res = mergeTwoSortedLists(l1, l2);
 81         /**  test  mergeTwoSortedLists  start ************/
 82         while (res.next != null) {// res is destroyed
 83             System.out.print(res.val + "\t");
 84             res = res.next;
 85         }
 86         System.out.println(res.val);
 87         System.out.println("After merge");
 88         /** End ***********************************/
 89         /** test removeNthFromEnd  start **************/
 90         showData(l1, l2);
 91         // use l2 to test
 92         int n = 1;
 93         l2 = removeNthFromEnd(l2,n);
 94         showData(l1, l2);
 95         /** End ***********************************/
 96     }
 97     /**
 98      * Print the ListNode
 99      * @param l1 ListNode
100      * @param l2 ListNode
101      */
102     public static void showData(ListNode l1, ListNode l2){
103         System.out.println("l1 -->");
104         while (l1.next != null) {
105             System.out.print(l1.val + "\t");
106             l1 = l1.next;
107         }
108         System.out.println(l1.val);
109         System.out.println("l2 -->");
110         while (l2.next != null) {
111             System.out.print(l2.val + "\t");
112             l2 = l2.next;
113         }
114         System.out.println(l2.val);
115         System.out.println("/************************************/");
116     }
117 }
118 
119 //Definition for singly-linked list.
120 class ListNode {
121     int val;
122     ListNode next;
123     ListNode(int x) { val = x; }
124 }      

輸出：

input List l1 and l2

l1 -->

0 2 4 6 8 10

l2 -->

1 3 5 7 9

/************************************/

mergeTwoLists(l1, l2) -->

0 1 2 3 4 5 6 7 8 9 10

After merge

1 2 3 4 5 6 7 8 9 10

9

0 1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9