删除链表中重复的结点

题目描述

解题描述

代码语言：javascript复制

public class DeleteDuplicationInList {

    static class ListNode {
        public ListNode next;
        public Integer val;
    }

    /**
     * 只能删除连续的的重复数字
     * @param pHead
     * @return
     */
    public ListNode deleteDuplication(ListNode pHead) {
        if (pHead == null || pHead.next == null) { // 只有0个或1个结点，则返回
            return pHead;
        }
        if (pHead.val.equals(pHead.next.val)) { // 当前结点是重复结点
            ListNode pNode = pHead.next;
            while (pNode != null && pNode.val.equals(pHead.val)) {
                // 跳过值与当前结点相同的全部结点,找到第一个与当前结点不同的结点
                pNode = pNode.next;
            }
            return deleteDuplication(pNode); // 从第一个与当前结点不同的结点开始递归
        } else { // 当前结点不是重复结点
            pHead.next = deleteDuplication(pHead.next); // 保留当前结点，从下一个结点开始递归
            return pHead;
        }
    }

    /**
     * 删除所有重复的节点
     * @param pHead
     * @return
     */
    public ListNode deleteDuplication2(ListNode pHead) {
        if (pHead == null) {
            return null;
        }
        // 先找出相同结点，存入 set
        HashSet<Integer> set = new HashSet<>();
        ListNode pre = pHead;
        ListNode cur = pHead.next;
        while (cur != null) {
            if (cur.val.equals(pre.val)) {
                set.add(cur.val);
            }
            pre = cur;
            cur = cur.next;
        }
        // 再根据相同节点删除
        // 先删头部
        while (pHead != null && set.contains(pHead.val)) {
            pHead = pHead.next;
        }
        if (pHead == null) {
            return null;
        }
        // 再删中间结点
        pre = pHead;
        cur = pHead.next;
        while (cur != null) {
            if (set.contains(cur.val)) {
                pre.next = cur.next;
            } else {
                pre = cur;
            }
            cur = cur.next;
        }
        return pHead;
    }

    public static void main(String[] args) {
        ListNode first = new ListNode();
        first.val = 1;
        ListNode second = new ListNode();
        second.val = 2;
        ListNode third = new ListNode();
        third.val = 2;
        ListNode four = new ListNode();
        four.val = 3;
        ListNode five = new ListNode();
        five.val = 2;
        ListNode six = new ListNode();
        six.val = 5;
        first.next = second;
        second.next = third;
        third.next = four;
        four.next = five;
        five.next = six;
        ListNode listNode = new DeleteDuplicationInList().deleteDuplication2(first);
        System.out.println(listNode.val);
        ListNode next = listNode.next;
        while (null != next) {
            System.out.println(next.val);
            next = next.next;
        }
    }
}

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