Javascript(leetcode#82) Remove Duplicates from Sorted List II

Difficult:Medium

題目

Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well.

翻譯

給定一個排序鍊錶的頭部，刪除所有具有重複數字的節點，只留下原始鍊錶中不同的數字。返回排序好的鍊錶。

範例

Example 1:

Input: head = [1,2,3,3,4,4,5]
Output: [1,2,5]

Example 2:

Input: head = [1,1,1,2,3]
Output: [2,3]

解題思路

1.設當前及上一個node和存放開頭的變數
2.當遇到相同值時，依序往前比較
3.如pre還是空時，將開頭直接等於next

Solution

var deleteDuplicates = function (head) {
    if (head == null) {
        return head;
    }
    let cur = head;
    let headnode = head;
    let pre = null;
    while (cur != null && cur.next != null) {
        if (cur.val == cur.next.val) {
            let next = cur.next;
            while (next != null && next.val == cur.val) {
                next = next.next;
            }
            if (pre == null) {
                headnode = next;
                cur = next;
            } else {
                pre.next = next;
                cur = next;
            }
        } else {
            pre = cur;
            cur = cur.next;
        }
    }
    return headnode;
};