README.md

217. 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.

Example 1:

Input: [1,2,3,1]
Output: true

Example 2:

Input: [1,2,3,4]
Output: false

Example 3:

Input: [1,1,1,3,3,4,3,2,4,2]
Output: true

Solutions (Java)

1. Linear Search

class Solution {
    public boolean containsDuplicate(int[] nums) {
        for(int i = 0; i < nums.length; ++i){
            for(int j = 0; j < i; j++){
                if(nums[i] == nums[j])
                    return true;
            }
        }
        return false;
    }
}

2. Sort

class Solution {
    public boolean containsDuplicate(int[] nums) {
        Arrays.sort(nums);
        for(int i = 0; i < nums.length - 1; ++i){
            if(nums[i] == nums[i + 1])
                return true;
        }
        return false;
    }
}

3. Hash Table

class Solution {
    public boolean containsDuplicate(int[] nums) {
        Set<Integer> set = new HashSet<>(nums.length);
        for(int x: nums){
            if(!set.add(x)){
                return true;
            }
        }
        return false;
    }
}