Real-time 1v1

Race someone.
Not the clock.

You and one opponent get the same Codeforces problem at the same instant. Their tests pass in front of you as you type. You never see a line of their code. First correct solution wins.

Problems
109
Rating
800–1200
Languages
3
Hidden tests
1,870
Live duel21 tests
you21/21 · Accepted
for i in range(n):
    total += a[i] * 2
opponent14/21 · Wrong answer
code hidden

Illustrative. You always see how far they have got — never how they got there.