1️⃣.从头到尾的链表反转
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class Solution {
public ListNode reverseList(ListNode head) {
ListNode pre =null;
ListNode curr = head;
while(curr!=null){
ListNode next = curr.next;
curr.next = pre;
pre = curr;
curr = next;
}
return pre;
}
}
2️⃣.给定区间的链表反转
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class Solution {
public ListNode reverseBetween(ListNode head, int left, int right) {
ListNode temp = new ListNode(0,head);
ListNode pre =temp;
//找到要反转节点 前面那个节点
int r=1;
while(r<left){
pre = pre.next;
++r;
}
ListNode curr = pre.next;
for(int i=1;i<=right-left;++i){
ListNode next = curr.next;
curr.next = next.next;
next.next = pre.next;
pre.next = next;
}
return temp.next;
}
}
3️⃣. 2个一组的链表反转
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class Solution {
//两个一组反转链表
public ListNode swapPairs(ListNode head) {
ListNode pre = new ListNode(0,head);
ListNode temp = pre;
while(pre.next!=null&&pre.next.next!=null){
ListNode n1 = pre.next;
ListNode n2 = pre.next.next;
pre.next = n2;
n1.next = n2.next;
n2.next = n1;
pre = n1;
}
return temp.next;
}
}
4️⃣. k个一组的链表反转
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class Solution {
//k个一组反转链表
public ListNode reverseKGroup(ListNode head, int k) {
ListNode temp = new ListNode(0,head);
ListNode end = temp;
ListNode pre = temp;
while(end.next!=null){
for(int i=1;i<=k&&end!=null;i++){
end =end.next;
}
if(end==null) break;
ListNode start = pre.next;
ListNode next = end.next;
end.next=null;
pre.next = reverse(start);
start.next =next;
pre =start;
end =pre;
}
return temp.next;
}
public ListNode reverse(ListNode head){
ListNode pre = null;
ListNode curr = head;
while(curr!=null){
ListNode next = curr.next;
curr.next = pre;
pre=curr;
curr=next;
}
return pre;
}
}
总结提炼🎯
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1️⃣要舍得用指针