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Example analysis of Java implementation of printing linked list from end to beginning

黄舟
Release: 2017-10-16 09:51:59
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This article mainly introduces Java programming to implement an example of printing a linked list code from the end to the beginning. The editor thinks it is quite good, so I will share it with you here for the reference of friends who need it.

Problem description: Enter the head node of a linked list, and print the value of each node in reverse from the tail to the head.

First define the linked list nodes


public class ListNode {
    int val;
    ListNode next = null;
    ListNode(int val){
      this.val = val;
    }
  }
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Idea 1: This question obviously uses the idea of ​​​​the stack, last in first out, First traverse the linked list and push the node values ​​onto the stack in sequence. Finally, pop the stack after traversing the stack.


public static Stack<Integer> printListReverse_Stack(ListNode listNode){
    Stack<Integer> stack = new Stack<Integer>();
    if(listNode != null){
      ListNode p = listNode;
      while(p != null){
        stack.add(p.val);
        p = p.next;
      }
    }
    return stack;
  }
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Idea 2: Traverse the linked list directly and insert it into the ArrayList sequentially according to the head insertion method


public static ArrayList<Integer> printListFromTailToHead(ListNode listNode){//表头也存储元素
    ArrayList<Integer> print = new ArrayList<Integer>();
    if(listNode == null){
      return print;
    }
    int add = 0;
    ListNode p = listNode;
    while(p != null){
      print.add(0, p.val);
      p = p.next;
    }
    return print;
  }
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Idea 3: You can use the idea of ​​recursion (the essence is also the idea of ​​stack)


public ArrayList<Integer> printListReversely_Recursively(ListNode listNode){
    ArrayList<Integer> print = new ArrayList<Integer>();
    if(listNode == null){
      return print;
    }
    print.addAll(printListReversely_Recursively(listNode.next));
    print.add(listNode.val);
    return print;
  }
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