LeetCode #10

What I’ve Learned

First, when reversing the LinkedList, you can define the after variable inside while loop.

Disclaimer

My LeetCode is free plan. I am posting just the free algorithms for now on. Also, I am using JAVA to code.

344. Reverse String

My Solution

I solved this problem and the solution was clear. I wasn’t able to come up with 2 pointers but I didn’t see the solutions. I am proud.

class Solution {
    public void reverseString(char[] s) {
        char temp = 'a';
        for(int i =0; i<s.length/2;i++) {
        	temp = s[i];
        	s[i] = s[s.length-1-i]; 
        	s[s.length-1-i]= temp;
        }
    }
}

206. Reverse Linked List

My Solution

I’ve saw this problem in Udemy. I know how to do it but I wasn’t able to fix it due to the return. Also, defining ListNode after = temp.next; is a good idea I think.

class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode before = null;
        ListNode temp = head;


        while(temp != null){
            ListNode after = temp.next;
            temp.next = before;
            before = temp;
            temp = after;
        }
        return before;
    }
}

141. Linked List Cycle

My Solution

I’ve also saw this question in Udemy. I thought it would be easy to solve, but the problem was using while loop.

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

    }
}