Find the missing element in an unsorted array where every element?

Short answer: appears twice except one public int SingleNumber(int[] nums) {

Example code

int result = 0;
foreach (var num in nums) {
result ^= num;
}
return result;
} Explanation: XOR of all elements cancels duplicates, leaving the single unique element.

Real-world example (ShopNest)

In coding rounds, state complexity aloud, write a clear ShopNest-flavored example (orders, carts), then handle edge cases (empty list, null, overflow).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.