Cracking a “perfect deduction” lock puzzle, one clue at a time. Start with the heavy hitters: 738 tells us none of those digits appear anywhere. Then 780 says exactly one digit is correct but misplaced—so the 0 is in, just not in the last spot. Compare the clues, eliminate contradictions, and the whole thing unravels cleanly: 0 must lead, 2 belongs third, and 4 fills the middle. Final combo: 042. And the twist? If “one number is correct” means at least one, a second solution opens up. That’s the