#0248

Single Number with XOR

EasyDSA18 min10 XP

Problem

Given nums where exactly one value appears once and every other value appears twice, return the single value.

Why This Matters

This is the simplest useful XOR identity: duplicates cancel out without extra memory.

Function Signature

def single_number(nums):

Examples

Example 1

Inputnums = [4, 1, 2, 1, 2]

Output4

1 and 2 cancel themselves through XOR, leaving 4.

Constraints

Return the exact requested value.
Handle empty or small inputs when the prompt allows them.
Prefer the target DSA pattern over brute force when the input can grow.

CodePython

def single_number(nums):
    """
    Input example: nums = [4, 1, 2, 1, 2]
    Return: 4
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return 0

def single_number(nums):
    """
    Input example: nums = [4, 1, 2, 1, 2]
    Return: 4
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return 0

Visible browser tests run here when available.

Testcases2 visible / 3 hidden categories

Middle duplicates

Input[4, 1, 2, 1, 2]

Expected4

Only 4 appears once.

Single element

Input[9]

Expected9

The only element is the answer.

Hidden Test Categories

negative numberssingle number at endlarge duplicate set