主要是記錄中間狀態, before以及after兩個指針。另外注意終止條件:while(before->next!= NULL && before->next->next!=NULL){ 避免報錯。
另外還有別人總結的遞歸的騷解法。
// 我的解法
class Solution {
public:
ListNode* swapPairs(ListNode* head) {
if(head == NULL) return NULL;
if(head->next == NULL) return head;
ListNode* before = new ListNode(-1);
ListNode* after = new ListNode(-1);
ListNode* all = before;
before->next = head;
while(before->next!= NULL && before->next->next!=NULL){
after = before->next->next->next;
before->next->next->next = before->next;
before->next = before->next->next;
before->next->next->next = after;
before = before->next->next;
}
return all->next;
}
};
//按照別人的提示的遞歸的解法
class Solution {
public:
ListNode* swapPairs(ListNode* head) {
if(head == NULL || head->next == NULL) return head;
ListNode* head_next = head->next;
head->next = swapPairs(head_next->next);
head_next->next = head;
return head_next;
}
};