Suppose you want to move from to on the number line. In each step, you either move right by a unit distance or you take a shortcut. A shortcut is simply a pre-specified pair of integers . Given a shortcut , if you are at position on the number line, you may directly move to . Suppose denotes the smallest number of steps needed to move from to . Suppose further that there is at most shortcut involving any number, and in particular, from there is a shortcut to . Let and be such that . Then the value of the product is _____.
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Answer: 150
To find the minimum number of steps to reach from any position , we analyze the choices available at position .
At any position , we can always make a standard move of unit to the right, reaching . Additionally, if there is a shortcut starting at to some destination , we can also choose to jump directly to .
For :
- Standard move: Move unit right to reach . The remaining steps needed would be .
- Shortcut move: We are given that there is a shortcut from to . Taking this shortcut leads to position . The remaining steps needed would be .
Since we want to minimize the number of steps, the optimal choice from is given by the recurrence:
Comparing this with the given equation:
We identify that the set of values for is .
Thus, the product is:
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