Leetcode 6

LinkedList Easy

1. 83. Remove Duplicates from Sorted List

　　当前节点值如果和下一个节点值相同直接略过。

class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if( head == null)
            return null;
        ListNode node = head;
        while( node.next != null){
            if(node.next.val == node.val){
                node.next = node.next.next;
            }
            else
                node = node.next;
        }
        return head;
    }
}

2. 141. Linked List Cycle

　　用快慢针，如果有循环快慢针会在某一时刻相同

public class Solution {
    public boolean hasCycle(ListNode head) {
        if( head == null || head.next == null)
            return false;
        ListNode fast = head;
        ListNode slow = head;
        while( fast != null && fast.next != null){
            slow = slow.next;
            fast = fast.next.next;
            if( slow == fast)
                return true;
        }
        return false;
    }
}

3. 234. Palindrome Linked List

　　用快慢针找到链表重点，我们可以在找到中点后，将后半段的链表翻转一下，这样我们就可以按照回文的顺序比较了。

class Solution {
    public boolean isPalindrome(ListNode head) {
        if( head == null || head.next == null)
            return true;
        ListNode fast = head;
        ListNode slow = head;
        while(fast.next !=null && fast.next.next !=null){
            slow = slow.next;
            fast = fast.next.next;
        }
        ListNode pre = head, last = slow.next;
        while( last.next != null){
            ListNode temp = last.next;
            last.next = temp.next;
            temp.next = slow.next;
            slow.next = temp;
        }
        while(slow.next != null){
            slow = slow.next;
            if(pre.val != slow.val)
                return false;
            pre = pre.next;
        }
        return true;
    }
}