Description:
Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.
Examples:
Example 1:
Input: nums = [1,2,3,1]
Output: true
Example 2:
Input: nums = [1,2,3,4]
Output: false
Example 3:
Input: nums = [1,1,1,3,3,4,3,2,4,2]
Output: trueSolution in Python:
Python
from typing import List
class Solution:
def containsDuplicate(self, nums: List[int]) -> bool:
# Initialize a set to keep track of seen numbers
seen = set()
# Iterate through each number in the array
for num in nums:
# If the number is already in the set, we found a duplicate
if num in seen:
return True
# Otherwise, add the number to the set
seen.add(num)
# If no duplicates were found, return False
return False
# Example usage
sol = Solution()
print(sol.containsDuplicate([1, 2, 3, 1])) # Output: True
print(sol.containsDuplicate([1, 2, 3, 4])) # Output: False
print(sol.containsDuplicate([1, 1, 1, 3, 3, 4, 3, 2, 4, 2])) # Output: TrueExplanation:
- Initialization:
- A set named
seenis initialized to keep track of the numbers that have been encountered as we iterate through the array. Sets are used because they provide an average-case time complexity of O(1) for both insertions and lookups.
- A set named
- Iteration:
- We iterate through each number in the
numsarray.
- We iterate through each number in the
- Checking for Duplicates:
- For each number, we check if it is already in the
seenset. - If it is, this means the number has appeared before, so we return
Trueto indicate that there is at least one duplicate in the array. - If it is not in the set, we add the number to the
seenset and continue iterating.
- For each number, we check if it is already in the
- Completion:
- If the loop completes without finding any duplicates, we return
False.
- If the loop completes without finding any duplicates, we return
Example Execution:
- For
nums = [1, 2, 3, 1]:- Iteration 1:
num = 1,seen = {1} - Iteration 2:
num = 2,seen = {1, 2} - Iteration 3:
num = 3,seen = {1, 2, 3} - Iteration 4:
num = 1, since1is inseen, returnTrue.
- Iteration 1:
- For
nums = [1, 2, 3, 4]:- Iteration 1:
num = 1,seen = {1} - Iteration 2:
num = 2,seen = {1, 2} - Iteration 3:
num = 3,seen = {1, 2, 3} - Iteration 4:
num = 4,seen = {1, 2, 3, 4} - No duplicates found, return
False.
- Iteration 1:
- For
nums = [1, 1, 1, 3, 3, 4, 3, 2, 4, 2]:- Iteration 1:
num = 1,seen = {1} - Iteration 2:
num = 1, since1is inseen, returnTrue.
- Iteration 1:
Solution in Javascript:
JavaScript
/**
* @param {number[]} nums
* @return {boolean}
*/
var containsDuplicate = function(nums) {
// Initialize a set to keep track of seen numbers
let seen = new Set();
// Iterate through each number in the array
for (let num of nums) {
// If the number is already in the set, we found a duplicate
if (seen.has(num)) {
return true;
}
// Otherwise, add the number to the set
seen.add(num);
}
// If no duplicates were found, return false
return false;
};
// Example usage
console.log(containsDuplicate([1, 2, 3, 1])); // Output: true
console.log(containsDuplicate([1, 2, 3, 4])); // Output: false
console.log(containsDuplicate([1, 1, 1, 3, 3, 4, 3, 2, 4, 2])); // Output: trueSolution in Java:
Java
import java.util.HashSet;
import java.util.Set;
class Solution {
public boolean containsDuplicate(int[] nums) {
// Initialize a set to keep track of seen numbers
Set<Integer> seen = new HashSet<>();
// Iterate through each number in the array
for (int num : nums) {
// If the number is already in the set, we found a duplicate
if (seen.contains(num)) {
return true;
}
// Otherwise, add the number to the set
seen.add(num);
}
// If no duplicates were found, return false
return false;
}
// Example usage
public static void main(String[] args) {
Solution sol = new Solution();
System.out.println(sol.containsDuplicate(new int[]{1, 2, 3, 1})); // Output: true
System.out.println(sol.containsDuplicate(new int[]{1, 2, 3, 4})); // Output: false
System.out.println(sol.containsDuplicate(new int[]{1, 1, 1, 3, 3, 4, 3, 2, 4, 2})); // Output: true
}
}Solution in C#:
C#
using System;
using System.Collections.Generic;
public class Solution {
public bool ContainsDuplicate(int[] nums) {
// Initialize a HashSet to keep track of seen numbers
HashSet<int> seen = new HashSet<int>();
// Iterate through each number in the array
foreach (int num in nums) {
// If the number is already in the set, we found a duplicate
if (seen.Contains(num)) {
return true;
}
// Otherwise, add the number to the set
seen.Add(num);
}
// If no duplicates were found, return false
return false;
}
}