I interviewed with Facebook last month and got one interesting question:\n\nSpread secret:\n[A, B, 10]\n[A, C, 20]\n[B, D, 30]\n[B, E, 5]\n\nSource of secret: A\n\nHere input means A talks to B and spread secret at time 10,etc.\nThus C will know secret at time 20, D will know at time 30.\nHowever E doesnt\' know because B talks to E at time 5 when B himself doesn\'t know secret.\nThus return a list of people who will know the secret at the end of day, answer will be [A, B, C, D]\n\nI think this is not easy but also not hard. Solve it with BFS, just to compare time order when pushing into queue.\n\nAnd now it\'s follow-up:\nIt\'s still the same relationship input, but now we know eventually it\'s [A, B, C, D] that get to know the secret, can you please return who\'s the source of secret? (Can be one or multiple)\nAny thoughts on the follow-up question?

I interviewed with Facebook last month and got one interesting question:\n\nSpread secret:\n[A, B, 10]\n[A, C, 20]\n[B, D, 30]\n[B, E, 5]\n\nSource of secret: A