030 Digit fifth powers.sf

#!/usr/bin/ruby

# Author: Trizen
# Date: 18 March 2023
# https://github.com/trizen

# https://projecteuler.net/problem=30

# Runtime: 11.792s

# The limit can be found by solving for `k` in the inequality:
#  10^k > k * 9^5

var k = bsearch_inverse(0, 10, {|k|
    10**k <=> k*9**5
})

say (2 .. 10**k -> lazy.grep {|n| n.digits.sum_by { .ipow(5) } == n }.sum)