LeetCode【83. 删除排序链表中的重复元素】

版权声明： https://blog.csdn.net/qq_38386316/article/details/82901757

题目描述

给定一个 排序链表，删除所有重复的元素，使得每个元素之出现一次。

示例 * 1

• 输入: 1->1->2
• 输出: 1->2

示例 * 2

• 输入: 1->1->2->2->3->3
• 输出: 1->2->3

思路 * 1
使用一个listNode变量对其链表进行遍历，遍历时删除相邻的相等的元素，同时注意一下条件语句，需要 $head != null$ 和 $head.next != null$的顺序。
代码 * 1

class Solution {
    public ListNode deleteDuplicates(ListNode head){
        ListNode cur = new ListNode(-1);
        cur.next = head;
        while(head != null && head.next != null) {
            if(head.next.val == head.val) {
                head.next = head.next.next;
            }else {
                head = head.next;
            }
        }
        return cur.next;
    }
}

复杂度分析

• 时间复杂度 : $O(N)$
• 空间复杂度 : $O(1)$

思路 * 2：
将上面的代码改为递归的形式。
代码 * 2

class Solution {
    public ListNode deleteDuplicates(ListNode head){
        if(head == null || head.next == null) return head;
        head.next = deleteDuplicates(head.next);
        return head.next.val == head.val ? head.next : head;
    }
}

复杂度分析

• 时间复杂度 : $O(N)$
• 空间复杂度 : $O(N)$

完整代码

package leetcode83;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * Created by 张超帅 on 2018/9/29.
 */
class ListNode {
    int val;
    ListNode next;
    ListNode (int val) {
        this.val = val;
    }
}
class Solution {
    public ListNode deleteDuplicates(ListNode head){

        if(head == null || head.next == null) return head;
        head.next = deleteDuplicates(head.next);
        return head.next.val == head.val ? head.next : head;

    }
}
public class leetcode83 {
    public static int[] stringToArrays(String input) {
        input = input.trim();
        input = input.substring(1, input.length() - 1);
        if(input == null) {
            return new int[0];
        }
        String[] parts = input.split(",");
        int[] result = new int[parts.length];
        for(int i = 0; i < parts.length; i ++) {
            String part = parts[i].trim();
            result[i] = Integer.parseInt(part);
        }
        return result;
    }
    public static ListNode stringToListnode(String input) {
        int[] nodeValues = stringToArrays(input);
        ListNode dummpy = new ListNode(-1);
        ListNode cur = dummpy;
        for(int value : nodeValues) {
            cur.next = new ListNode(value);
            cur = cur.next;
        }
        return dummpy.next;
    }
    public static String listnodeToString(ListNode ret){
        if(ret == null) {
            return "[]";
        }
        String s = "";
        while(ret != null) {
            s = s + ret.val + ", ";
            ret = ret.next;
        }
        return "[" + s.substring(0, s.length() - 2) + "]";
    }
    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String line;
        while((line = in.readLine()) != null) {
            ListNode head = stringToListnode(line);
            ListNode ret = new Solution().deleteDuplicates(head);
            String out = listnodeToString(ret);
            System.out.println(out);
        }
    }
}