Coding intervew: 链表反转

单向链表反转

static class Node {
        Node next;
        int val;

        Node(int v){
            this.val  = v;
        }
    }

    public static Node reverse(Node head) {
        Node pre = null;
        Node cur = head;
        Node next = null;

        while(cur != null) {
            next= cur.next;
            cur.next = pre;
            pre = cur;
            cur = next;
        }
        return pre;
    }

双向链表反转

static class Node {
        Node last;
        Node next;
        int val;
        Node(int v){
            val = v;
        }
    }


    public static Node reverse(Node head){
        Node pre = null;
        Node cur = head;
        Node next = null;

        while(cur!=null){
            next = cur.next;
            cur.next = pre;
            cur.last = next;
            pre = cur;
            cur = next;
        }
        return pre;
    }

单向链表反转部分

public static Node reversePart(Node head,int from, int to) {
        int len = 0;
        Node p = head;
        Node fPre = null,tPos = null;
        while(p!=null){
            len++;
            fPre = len==from-1?p:fPre;
            tPos = len==to+1?p:tPos;
            p=p.next;
        }

        if(from<1||to>len) {
            return head;
        }

        Node pre = tPos;
        Node cur = fPre==null?head:fPre.next;
        Node next = null;
        while(cur!=tPos){
            next = cur.next;
            cur.next = pre;
            pre = cur;
            cur = next;
        }
        if(fPre!=null){
            fPre.next = pre;
            return head;
        }else{
            return pre;
        }
    }