Yahoo Interview Questions

Question: Contains Duplicate

//Given an array of integers, find if the array contains any duplicates. Your function should return 
//true if any value appears at least twice in the array, and it should return false if every element is distinct.
class ContainsDuplicate {
    public boolean containsDuplicate(int[] nums) {
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        for(int i: nums) {
            if(map.containsKey(i)) {
                return true;
            } else {
                map.put(i, 1);
            }
        }
        
        return false;
    }
}

Question: Linked List Cycle

//Given a linked list, determine if it has a cycle in it.
//Follow up:
//Can you solve it without using extra space?
/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public boolean hasCycle(ListNode head) {
        if(head == null || head.next == null) {
            return false;
        }
        
        ListNode slow = head;
        ListNode fast = head.next;
        while(fast != null && fast.next != null && fast != slow) {
            slow = slow.next;
            fast = fast.next.next;
        }
        
        return fast == slow;
    }
}