搞定面试中的链表题目(Java实现)

灰太狼 2022-05-24 12:46 158阅读 0赞

**本文转载自：https://www.jianshu.com/p/a64d1ef95980**

这是一篇关于链表的文章，总结了链表数据结构和算法相关的一些题目。  
先上链表的数据结构：

class ListNode {
        ListNode next;
        int val;
        ListNode(int x){
            val = x;
            next = null;
        }
    }

### 1.翻转链表 ###

ListNode reverse(ListNode node){
            ListNode prev = null;
            while(node!=null){
                ListNode tmp = node.next;
                node.next = prev;
                prev = node;
                node = tmp;
            }
            return prev;
        }
        //翻转链表(递归方式)
        ListNode reverse2(ListNode head){
            if(head.next == null){
                return head;
            }
            ListNode reverseNode = reverse2(head.next);
            head.next.next = head;
            head.next = null;
            return reverseNode;
            
        }

### 2.判断链表是否有环 ###

boolean hasCycle(ListNode head){
            if(head == null|| head.next == null){
                return false;
            }
            ListNode slow,fast;
            fast = head.next;
            slow = head;
            while(fast!=slow){
                if(fast==null||fast.next==null){
                    return false;
                }
                fast = fast.next.next;
                slow = slow.next;
            }
            return true;
        }

### 3,链表排序 ###

ListNode sortList(ListNode head){
            if(head == null|| head.next == null){
                return head;
            }
            ListNode mid = middleNode(head);
            ListNode right = sortList(mid.next);
            mid.next = null;
            ListNode left = sortList(head);
            return merge(left, right);
        }
        ListNode middleNode(ListNode head){
            ListNode slow = head;
            ListNode fast = head.next;
            while(fast!=null&fast.next!=null){
                slow = slow.next;
                fast = fast.next.next;
            }
            return slow;
        }
        ListNode merge(ListNode n1,ListNode n2){
            ListNode dummy = new ListNode(0);
            ListNode node = dummy;
            while (n1!=null&&n2!=null) {
                if(n1.val<n2.val){
                    node.next = n1;
                    n1 = n1.next;
                }else{
                    node.next = n2;
                    n2 = n2.next;
                }
                node = node.next;
            }
            if(n1!=null){
                node.next = n1;
            }else{
                node.next = n2;
            }
            return dummy.next;
        }

### 4.链表相加求和 ###

ListNode addLists(ListNode l1,ListNode l2){
            if(l1==null&&l2==null){
                return null;
            }
            ListNode head = new ListNode();
            ListNode point = head;
            int carry = 0;
            while(l1!=null&&l2!=null){
                int sum = carry + l1.val + l2.val;
                point.next = new ListNode(sum%10);
                carry = sum/10;
                l1 = l1.next;
                l2 = l2.next;
                point = point.next;
            }
            while(l1!=null){
                int sum = carry + l1.val;
                point.next = new ListNode(sum%10);
                carry = sum/10;
                l1 = l1.next;
                point = point.next;
            }
            while(l2!=null){
                int sum = carry + l2.val;
                point.next = new ListNode(sum%10);
                carry = sum/10;
                l2 = l2.next;
                point = point.next;
            }
            if(carry!=0){
                point.next = new ListNode(carry);
                
            }
            return head.next;
        }

### 5.得到链表倒数第n个节点 ###

ListNode nthToLast(ListNode head,int n ){
            if(head == null||n<1){
                return null;
            }
            ListNode l1 = head;
            ListNode l2 = head;
            for(int i = 0;i<n-1;i++){
                if(l2 == null){
                    return null;
                }
                l2 = l2.next;
            }
            while(l2.next!=null){
                l1 = l1.next;
                l2 = l2.next;
            }
            return l1;
            
            
        }

### 6.删除链表倒数第n个节点 ###

ListNode deletenthNode(ListNode head,int n){
            // write your code here
            if (n <= 0) {
                return null;
            }
            
            ListNode dumy = new ListNode(0);
            dumy.next = head;
            ListNode prdDel = dumy;
            for(int i = 0;i<n;i++){
                if(head==null){
                    return null;
                }
                head = head.next;
            }
            while(head!=null){
                head = head.next;
                prdDel = prdDel.next;
            }
            prdDel.next = prdDel.next.next;
            return dumy.next;
            
        }

### 7.删除链表中重复的元素 ###

ListNode deleteMuNode(ListNode head){
            if(head == null){
                return null;
            }
            ListNode node = head;
            while(node.next != null){
                if(node.val == node.next.val){
                    node.next = node.next.next;
                }else{
                    node = node.next;
                }
            }
            return head;
            
        }

### 8.删除链表中重复的元素ii,去掉重复的节点 ###

ListNode deleteMuNode2(ListNode head){
            if(head == null||head.next == null){
                return head;
            }
            ListNode dummy = new ListNode(0);
            dummy.next = head;
            head = dummy;
            while(head.next!=null&&head.next.next!=null){
                if(head.next.val == head.next.next.val){
                    int val = head.next.val;
                    while(head.next.val == val&&head.next != null){
                        head.next = head.next.next;
                    }
                }else{
                    head = head.next;
                }
            }
            return dummy.next;
        }

### 9.旋转链表 ###

ListNode rotateRight(ListNode head,int k){
            if(head ==null){
                return null;
            }
            int length = getLength(head);
            k = k % length;
            ListNode dummy = new ListNode(0);
            dummy.next = head;
            head = dummy;
            ListNode tail = dummy;
            for(int i = 0;i<k;i++){
                head = head.next;
            }
            while(head.next!= null){
                head = head.next;
                tail = tail.next;
            }
            head.next = dummy.next;
            dummy.next = tail.next;
            tail.next = null;
            return dummy.next;
        }

### 10.重排链表 ###

ListNode reOrder(ListNode head){
            if(head == null||head.next == null){
                return;
            }
            ListNode mid = middleNode(head);
            ListNode tail = reverse(mid.next);
            mergeIndex(head, tail);
        }
        private void mergeIndex(ListNode head1,ListNode head2){
            int index = 0;
            ListNode dummy = new ListNode(0);
            while (head1!=null&&head2!=null) {
                if(index%2==0){
                    dummy.next = head1;
                    head1 = head1.next;
                }else{
                    dummy.next = head2;
                    head2 = head2.next;
                }
                dummy = dummy.next;
                index ++;
            }
            if(head1!=null){
                dummy.next = head1;
            }else{
                dummy.next = head2;
            }
        }

### 11.链表划分 ###

ListNode partition(ListNode head,int x){
            if(head == null){
                return null;
            }
            ListNode left = new ListNode(0);
            ListNode right = new ListNode(0);
            ListNode leftDummy = left;
            ListNode rightDummy = right;
            while(head!=null){
                if(head.val<x){
                    left.next = head;
                    left = head;
                }else{
                    right.next = head;
                    right = head;
                }
                head = head.next;
            }
            left.next = rightDummy.next;
            right.next = null;
            return leftDummy.next;
        }

### 12.翻转链表的n到m之间的节点 ###

ListNode reverseN2M(ListNode head,int m,int n){
            if(m>=n||head == null){
                return head;
            }
            ListNode dummy = new ListNode(0);
            dummy.next = head;
            head = dummy;
            for(int i = 1;i<m;i++){
                if(head == null){
                    return null;
                }
                head = head.next;
            }
            ListNode pmNode = head;
            ListNode mNode = head.next;
            ListNode nNode = mNode;
            ListNode pnNode = mNode.next;
            for(int i = m;i<n;i++){
                if(pnNode == null){
                    return null;
                }
                ListNode tmp = pnNode.next;
                pnNode.next = nNode;
                nNode = pnNode;
                pnNode = tmp;
            }
            pmNode.next = nNode;
            mNode.next = pnNode;
            return dummy.next;
        }

### 13.合并K个排序过的链表 ###

ListNode mergeKListNode(ArrayList<ListNode> k){
            if(k.size()==0){
                return null;
            }
            return mergeHelper(k,0,k.size()-1);
        }
        ListNode mergeHelper(List<ListNode> lists,int start,int end){
            if(start == end){
                return lists.get(start);
            }
            int mid = start + ( end - start )/2;
            ListNode left = mergeHelper(lists, start, mid);
            ListNode right = mergeHelper(lists, mid+1, end);
            return mergeTwoLists(left,right);
        }
        ListNode mergeTwoLists(ListNode list1,ListNode list2){
            ListNode dummy = new ListNode(0);
            ListNode tail = dummy;
            while(list1!=null&&list2!=null){
                if(list1.val<list2.val){
                    tail.next = list1;
                    tail = tail.next;
                    list1 = list1.next;
                }else{
                    tail.next = list2;
                    tail = list2;
                    list2 = list2.next;
                }
                
            }
            if(list1!=null){
                tail.next = list1;
            }else{
                tail.next = list2;
            }
            return dummy.next;
        }

作者：IOExceptioner  
链接：https://www.jianshu.com/p/a64d1ef95980  
來源：简书  
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