s0024
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@ -1,11 +1,17 @@
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#include "s0024_swap_nodes_in_pairs.hpp"
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ListNode* S0024::swapPairs(ListNode* head) {
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// 只有当 head 和 head->next 都不为空时才翻转
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// 其它情况都直接返回
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if (head == nullptr || head->next == nullptr) {
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return head;
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}
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ListNode *newHead = head->next;
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head->next = swapPairs(newHead->next);
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newHead->next = head;
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return newHead;
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// 从这一行开始就假设 head 和 head->next 都不为空了
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// 我们首先把从 head->next->next 开始的链表翻转了
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ListNode* ptr = swapPairs(head->next->next);
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// 现在我们开始翻转 head 和 head->next
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ListNode* ans = head->next;
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head->next->next = head;
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head->next = ptr;
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return ans;
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}
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