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A-I: 0-9

A B C D
+ B C D
--------------
E F G H I
where each letter A-I represents different digit number 0-9.
Question:
Which number is absent in above ...

Tags: puzzle number

Counting Boolean Parenthesizations

You are given a boolean expression consisting of a string of the symbols 'true', 'false', 'and', 'or', and 'xor'. Count the number of ways to parenthesize the expression such that ...


Two-Person Traversal of a Sequence of Cities

You are given an ordered sequence of n cities, and the distances between every pair of cities. You must partition the cities into two subsequences (not necessarily contiguous) such that ...


Cube-free Words

Is there an infinite word on a two-letter alphabet in which no block occurs three times in succession?

Tags: math coding

Cut circle into pieces

Consider a loop of string of unit length. Suppose we cut the string independently and at random in n places. This will divide the loop into n pieces.

1. ...

Tags: to_study