Viewing insights from Codeforces 913G: Power Substring that are similar (thus shared) with only this insight from Codeforces 1860B: Fancy Coins: Be careful not to use brute force. The constraints are less than 10^8. Consider using floor division and modulus instead. by Solarion
- Consider it modulo a power of 10. by Solarion
- Say 10^50. Can you construct a number n modulo 5^50 such that 2^50 * n has the given substring? by Solarion
- Given this number n modulo 5^50, can you find r such that 2^r=n. This would solve the problem by Solarion
- This is the discrete logarithm problem, but here, we have that 2 is a primitive root mod 5^k for any k. by Solarion
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