Increasing Sequence Card Game
Time limit20sMemory limit1024 MB
For each N, compute the expected number of cards kept when a shuffled 1..N pile is scanned and a card is taken only if it exceeds the last taken card.
- Level
Medium6 of 10
- Topics
- Probability, Math, Dynamic programming, Combinatorics
- Solved
- No attempts yet
Problem
You are playing a card game by yourself.
There are N cards. The i-th card has the integer i written on it.
First you shuffle the N cards randomly and make them into a pile. You take the card at the top of the pile into your hand. Then you repeat the following process until the pile becomes empty:
- Check the card on the top of the pile.
- If the number on the card is larger than the number on the last card you took, take the card.
- Otherwise, discard the card.
The score of the game is the number of cards in your hand at the end. For a given number of cards N, what is the expected score of the game?
Input
The first line of the input contains the number of test cases, T. The next T lines follow. Each line contains a single integer N, the number of cards in the pile.
Output
For each test case, output one line containing Case #x: y, where x is the test case number (starting from 1) and y is the expected score at the end of the game.
y will be considered correct if it is within an absolute or relative error of 10-6 of the correct answer.
Limits
- 1 ≤ T ≤ 100.