import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代碼中的類名、方法名、參數(shù)名已經(jīng)指定，請勿修改，直接返回方法規(guī)定的值即可
     *
     * 
     * @param head ListNode類 
     * @return ListNode類
     */
    public ListNode deleteDuplicates (ListNode head) {
        // write code here
        if (head == null) return null;
        ListNode fast = head.next;
        ListNode slow = head;
        while(fast != null) {
            while(fast != null && fast.val == slow.val) fast = fast.next;
            slow.next = fast;
            slow = slow.next;
            if (fast != null) fast = fast.next;
        }
        return head;
    }
}

快慢指針越過相同元素