image 12 phase

A general overview of the “12 phases of mapping”! ~ A treasure trove of learning about counting problems - Qiita

• enumeration problem

• Given integers n and k greater than or equal to 0, how many ways are there to put n balls into k boxes?

  • There are 12 ways.
    • Whether n balls are distinguished from each other
    • Whether k boxes are distinguished from each other
    • The number of balls in each box can be “no more than one,” “no limit,” or “more than one.”

Difficult when not distinguishing between boxes. - Type II Sterling Number - number of bells - number of divisions

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