A b c 3 d July 8, 2019 16 32 64 128 A b c d 3 formula If a b 3 c d A b 2 3 c d 4 5 A b 2 c d 3 A 1 b 2 c 3 d 4 A 1 b 2 c 3 d A b c d e 3 A 3 b 3 c 3 d 3 leetcode A 3 b 4 c 5 d 6 A 3 b 4 c 5 d 6 e 7 A b c d 3 expansion A b c do 3 A b c 3 formula derivation
