剑指offer之反向打印链表值

1 问题

反向打印链表值

2 思考

1） 我们利用栈的思想，新进后出，把链表的每个元素分别入栈之后再打印栈

2）既然上面用到了栈，我们应该就会想到用到递归来实现

3 代码实现

#include <iostream>
#include <stack>
#include <stdlib.h>

using namespace std;

typedef struct node
{
  int value;
  struct node *next;
} Node;

/**
 *把链表的每一个元素遍历出来放进栈,然后利用
 *栈把先进后出的特点,然后打印栈
 */
void reverse_printf(Node *head)
{
  if (head == NULL)
  {
    std::cout << "head is NULL" << std::endl;
    return; 
  }
  Node *p = head;
  stack<Node *> stk;  
  while (p != NULL)
  {
    stk.push(p);
    p = p->next;
  }
  while(!stk.empty())
  {
    Node *node = stk.top();
    std::cout << node->value << std::endl;
    stk.pop();
  }
}

/**
 *既然上面用到了栈,那么我们自然而然就会想到
 *用递归的思想,我们就自己调用自己直到遍历到最后
 *很明显我们递归的条件是最后一个原始的next不能为空
 */
void reverse_printf1(Node *head)
{
  /**这样也行
  if (head == NULL)
  {
    return; 
  }
  reverse_printf1(head->next);
  std::cout << head->value << std::endl;**/
  if (head != NULL)
  {
    reverse_printf1(head->next);
    std::cout << head->value << std::endl;
  }
}


void printf(Node *head)
{
  if (head == NULL)
  {
    std::cout << "head is NULL" << std::endl;
    return; 
  }
  Node *p = head;
  while (p != NULL)
  {
    std::cout << p->value << std::endl;
    p = p->next;
  }
}

int main()
{
  Node *head = NULL;
  Node *node1 = NULL;
  Node *node2 = NULL;
  Node *node3 = NULL;
  head = (struct node*)malloc(sizeof(Node));
  node1 = (struct node*)malloc(sizeof(Node));
  node2 = (struct node*)malloc(sizeof(Node));
  node3 = (struct node*)malloc(sizeof(Node)); 
  if (head == NULL || node1 == NULL || node2 == NULL || node3 == NULL)
  {
    std::cout << "malloc fail" << std::endl;
    return -1;
  }
  head->value = 0;
  head->next = node1;

  node1->value = 1;
  node1->next = node2;

  node2->value = 2;
  node2->next = node3;

  node3->value = 3;
  node3->next = NULL;

  printf(head);
  std::cout << "***************" << std::endl;
  reverse_printf(head);
  std::cout << "***************" << std::endl;
  reverse_printf1(head);
  free(head);
  free(node1);
  free(node2);
  free(node3);
  return 0;

}

4 运行结果

0
1
2
3
***************
3
2
1
0
***************
3
2
1
0