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swap_nodes_in_pairs.cpp
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swap_nodes_in_pairs.cpp
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/*
* =====================================================================================
*
* Filename: swap_nodes_in_pairs.cpp
*
* Description: Swap Nodes in Pairs: Given a linked list, swap every two adjacent
* nodes and return its head.
*
* Version: 1.0
* Created: 07/10/18 11:12:21
* Revision: none
* Compiler: gcc
*
* Author: Zhu Xianfeng (), [email protected]
* Organization:
*
* =====================================================================================
*/
#include <stdio.h>
#include <stdlib.h>
#include <vector>
/**
* Definition for singly-linked list.
*/
struct ListNode
{
int val;
ListNode *next;
ListNode(int x) : val(x), next(NULL) {}
};
ListNode* createList(const std::vector<int>& nums)
{
ListNode* head = NULL;
ListNode* p = NULL;
ListNode* n = NULL;
for (size_t i = 0; i < nums.size(); i++)
{
n = new ListNode(nums[i]);
if (i == 0)
{
head = n;
}
else
{
p->next = n;
}
p = n;
}
return head;
}
void deleteList(ListNode* head)
{
ListNode* ptr = NULL;
while (head != NULL)
{
ptr = head->next;
delete head;
head = ptr;
}
}
void printList(ListNode* head)
{
ListNode* ptr = head;
while (ptr != NULL)
{
if (ptr != head)
{
printf(" -> ");
}
printf("%d", ptr->val);
ptr = ptr->next;
}
printf("\n");
}
// Non-recursive
class Solution1
{
public:
ListNode* swapPairs(ListNode* head)
{
if (head == NULL || head->next == NULL)
{
return head;
}
ListNode fake(0);
fake.next = head;
ListNode* p = &fake;
ListNode* q = p->next;
ListNode* r = q->next;
while (r != NULL)
{
q->next = r->next;
r->next = q;
p->next = r;
p = q;
q = p->next;
r = (q != NULL ? q->next : NULL);
}
return fake.next;
}
};
// Recursive
class Solution2
{
public:
ListNode* swapPairs(ListNode* head)
{
if (head == nullptr || head->next == nullptr)
{
return head;
}
auto* ptr = head->next;
head->next = swapPairs(head->next->next);
ptr->next = head;
return ptr;
}
};
using Solution = Solution2;
int main(int argc, char* argv[])
{
std::vector<int> nums = {1, 2, 3};
if (argc > 2)
{
nums.clear();
for (int i = 1; i < argc; i++)
{
nums.push_back(atoi(argv[i]));
}
}
ListNode* head = createList(nums);
printList(head);
head = Solution().swapPairs(head);
printList(head);
deleteList(head);
return 0;
}