remove_nth_node
remove_nth_node.cpp 源码
// 删除链表中倒数第 k 个节点
struct ListNode {
int val;
ListNode *next;
ListNode() : val(0), next(nullptr) {}
ListNode(int x) : val(x), next(nullptr) {}
ListNode(int x, ListNode *next) : val(x), next(next) {}
};
class Solution {
public:
// 两遍扫描
ListNode* removeNthFromEnd1(ListNode* head, int n) {
if (!head || !head->next) {
return nullptr;
}
int count = 0;
ListNode* c = head;
while (c) {
count++;
c = c->next;
}
if (count - n == 0) {
return head->next;
}
ListNode* prev = head, *p = head;
for (int i = 0; i < count - n; i++) {
prev = p;
p = p->next;
}
prev->next = prev->next->next;
return head;
}
// 快慢指针法
ListNode* removeNthFromEnd2(ListNode* head, int n) {
ListNode* fast = head;
for (int i = 0; i < n; ++i) {
fast = fast->next;
}
ListNode* dummy = new ListNode(-1);
dummy->next = head;
ListNode* slow = dummy;
while (fast != nullptr) {
slow = slow->next;
fast = fast->next;
}
slow->next = slow->next->next;
return dummy->next;
}
};
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