剑指Offer4
从尾到头打印链表
https://www.nowcoder.com/practice/d0267f7f55b3412ba93bd35cfa8e8035?tpId=13&tqId=11156&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github
题目
思路
Code
使用栈：
/**
* struct ListNode {
* int val;
* struct ListNode *next;
* ListNode(int x) :
* val(x), next(NULL) {
* }
* };
*/
class Solution {
public:
vector<int> printListFromTailToHead(ListNode* head) {
stack<int> a;
vector<int> res;
while(head)
{
a.push(head->val); //将元素入栈
head = head->next;
}
while(!a.empty()) //当栈中元素不为空时
{
res.push_back(a.top()); //读取栈顶元素放入vector向量
a.pop(); //弹出栈顶元素
}
return res;
}
}; 递归：
/**
* struct ListNode {
* int val;
* struct ListNode *next;
* ListNode(int x) :
* val(x), next(NULL) {
* }
* };
*/
class Solution {
public:
vector<int> printListFromTailToHead(ListNode* head) {
//使用递归实现
vector<int> res;
if(!head) //退出条件
return res;
res = printListFromTailToHead(head->next); //这里必须有res返回值
res.push_back(head->val);
return res;
}
}; reverse()函数：
class Solution {
public:
vector<int> printListFromTailToHead(ListNode* head) {
vector<int> res;
while(head)
{
res.push_back(head->val);
head = head->next;
}
reverse(res.begin(),res.end());
return res;
}
}; 
