Recursive solution: Use the special property of binary search tree: left sons are smaller while right sons are greater.

Super Straightforward.

if candies kinds > half of total, output the latter; otherwise the former.

Straightforward O(n).

Use two run and O(1) space.

Can use a stack to reduce to one run — O(n) space.

It isn’t really interesting.

Use SQL wildcard with like . % is any length. _ is one character.

Use dict to map charaters to row numbers.

Self explained.

1. Use XOR 11111… to flip bit.
2. Use Mask to decide which bits are 1s.

Straightforward.

Python string <-> ascii: ord() chr()

Sql if and case statement:

update [table] set [column] = if ([condition], [v1], [v2] )

(see case example at the end)