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]

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Intuition

Two approaches

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Sort the array, and check for consecutive duplicates

Time - O(N log N)

Space - O(1)

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Track elements in a set, and check for duplicates

Time - O(N)

Space - O(N)

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Related problems

219-contains-duplicate-ii

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

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	class Solution {
	public boolean containsDuplicate(int[] nums) {
	Set<Integer> set = new HashSet<Integer>();
	for (int i = 0; i < nums.length; i++) {
	if (set.contains(nums[i])) {
	return true;
	}
	set.add(nums[i]);
	}
	return false;
	}
	}

	class Solution:
	def containsDuplicate(self, nums: List[int]) -> bool:
	return len(set(nums)) != len(nums)

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