3 ms·

It does extend. It's just an XOR/parity trick. The last person shouts out the XOR of all the previous colors (if you prefer: whether the number of visible white

It does extend. It's just an XOR/parity trick. The last person shouts out the XOR of all the previous colors (if you prefer: whether the number of visible white hats is even or odd). From there, every other subsequent person knows their color by XORing the hats they see together with the guesses made so far. For example, the second to last person knows their hat is black (0) if the last person's guess matches the XOR of the hats they see - if it doesn't, their hat flipped it, and thus is white (1). And so on and so forth. Your hat color is everything you see and everything that was said XORed together.

huftis 9y ago
That’s correct. Or, to explain in (slightly) more non-mathematical terms: The last person (‘person 10’) shouts out (e.g.) ‘white’ if the number of white hats in front of him is an odd number (1, 3, 5, 7, 9) and ‘black’ otherwise. Let’s say he shouted ‘white’. The person in front of him looks at the people in front him. If it’s still an odd number of white hats, his must obviously be black; otherwise it must be white. If his hat is black, his shouts out ‘black’, and the person in front of him knows that the rest of the line (8 people) must still have an odd number of white hats, and he applies the exact same logic. But if the hat of person 9 was white, he would shout out ‘white’, and person 8 would know that the rest of the line (including himself) should now have an even number of white hats. So, basically the rule is: Define ‘the rest of the line’ to mean the people who have not yet shouted out a colour. When the first person (person 10) shouts out ‘white’, this means that ‘the rest of the line’ has an odd number of white hats (parity: odd). Whenever someone shouts out ‘white’, the parity (even/odd) of ‘the rest of the line’ is flipped. Using this, each person only has to count the number of white hats of the people in front of them and observe if it is even or odd. If it matches the parity of ‘the rest of the line’, the person’s hat is black, otherwise it’s white. (This also works for the person in front of the line (person 1). He sees no (or 0) white hats, i.e. he sees an even number of white hats.)

huftis 9y ago

That’s correct. Or, to explain in (slightly) more non-mathematical terms: The last person (‘person 10’) shouts out (e.g.) ‘white’ if the number of white hats in front of him is an odd number (1, 3, 5, 7, 9) and ‘black’ otherwise. Let’s say he shouted ‘white’. The person in front of him looks at the people in front him. If it’s still an odd number of white hats, his must obviously be black; otherwise it must be white. If his hat is black, his shouts out ‘black’, and the person in front of him knows that the rest of the line (8 people) must still have an odd number of white hats, and he applies the exact same logic. But if the hat of person 9 was white, he would shout out ‘white’, and person 8 would know that the rest of the line (including himself) should now have an even number of white hats. So, basically the rule is: Define ‘the rest of the line’ to mean the people who have not yet shouted out a colour. When the first person (person 10) shouts out ‘white’, this means that ‘the rest of the line’ has an odd number of white hats (parity: odd). Whenever someone shouts out ‘white’, the parity (even/odd) of ‘the rest of the line’ is flipped. Using this, each person only has to count the number of white hats of the people in front of them and observe if it is even or odd. If it matches the parity of ‘the rest of the line’, the person’s hat is black, otherwise it’s white. (This also works for the person in front of the line (person 1). He sees no (or 0) white hats, i.e. he sees an even number of white hats.)