How should I practice Extra Coin Win Probability?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Microsoft phone screen problems in FastPrep.

Is Extra Coin Win Probability associated with Microsoft?

FastPrep tags this as a Microsoft phone screen coding practice problem when the problem catalog has that company and stage context.

Extra Coin Win Probability

Microsoft● EasyFULLTIMEPHONE SCREEN

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Problem statement

Player A flips n + 1 independent fair coins, and player B flips n independent fair coins. Return the probability that A obtains strictly more heads than B.

Function

extraCoinWinProbability(n: int) → double

Examples

Example 1

n = 1return = 0.5

A's two coins beat B's one coin with probability one half.

Example 2

n = 100return = 0.5

The symmetry argument is independent of n.

Constraints

0 <= n <= 10^9
Results use absolute tolerance 1e-12