题目:
题解:
cpp
struct ListNode* middleNode(struct ListNode* head) {
struct ListNode* slow = head;
struct ListNode* fast = head;
while (fast->next != NULL && fast->next->next != NULL) {
slow = slow->next;
fast = fast->next->next;
}
return slow;
}
struct ListNode* reverseList(struct ListNode* head) {
struct ListNode* prev = NULL;
struct ListNode* curr = head;
while (curr != NULL) {
struct ListNode* nextTemp = curr->next;
curr->next = prev;
prev = curr;
curr = nextTemp;
}
return prev;
}
void mergeList(struct ListNode* l1, struct ListNode* l2) {
struct ListNode* l1_tmp;
struct ListNode* l2_tmp;
while (l1 != NULL && l2 != NULL) {
l1_tmp = l1->next;
l2_tmp = l2->next;
l1->next = l2;
l1 = l1_tmp;
l2->next = l1;
l2 = l2_tmp;
}
}
void reorderList(struct ListNode* head) {
if (head == NULL) {
return;
}
struct ListNode* mid = middleNode(head);
struct ListNode* l1 = head;
struct ListNode* l2 = mid->next;
mid->next = NULL;
l2 = reverseList(l2);
mergeList(l1, l2);
}