"Find the single non-repeated number where every other number appears twice."

Real-World Metaphor:

Think of matching socks. Every pair gets tossed into the laundry basket together. The one odd sock left alone on the table is your answer.

### The Mission Imagine a masquerade ballroom where everyone came in pairs wearing identical masks, except for **one single guest** who came alone! Given an array of integers where every number appears exactly twice except for one number that appears only once, identify the lone survivor. ### The XOR Magic Trick Any number XORed with itself cancels out to zero (`x ^ x = 0`). Any number XORed with zero stays itself (`x ^ 0 = x`). If you XOR every number together across the room, all pairs vaporize into zero, leaving **only the lone guest standing** in **O(N)** time and **O(1)** memory!

"Find the single non-repeated number where every other number appears twice."

Real-World Metaphor:

Think of matching socks. Every pair gets tossed into the laundry basket together. The one odd sock left alone on the table is your answer.

73. Single Number & The Lone Survivor

Single Number & The Lone Survivor

1. XOR Index 0 (4)

How to Think About This (Mental Model)

Examples