Leetcode Algorithm

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

My idea was pretty simple: Firstly, sort the array. And then loop through the array, if there are two consecutive elements the same, store the duplicated one in the empty array. Return whether the duplicate array is 0 or not.

Remember the loop starts from the index 1 as I am comparing the next index with the previous one, whose the smallest index is 0.

Python Solution:

# pythonclass Solution(object):
def containsDuplicate(self, nums):
:type nums: List[int]
:rtype: bool

dup = 0

for i in range(1, len(nums)):
if nums[i] == nums[i - 1]:
dup += 1
return dup != 0

JavaScript Solution:

* @param {number[]} nums
* @return {boolean}
var containsDuplicate = function(nums) {

dup = 0;


for (i = 1; i < nums.length; i++){
if (nums[i] == nums[i - 1]){
dup ++;


return dup != 0;



Special Thanks to Programmer Mitch, I learned a lot from his videos.




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