58. implement Diff<A, B>

  - accepted / - tried

Implement DiffKeys<A, B> to return the keys either in A or B, but not in both.

type A = DiffKeys<{a: 1, b: 2}, {b: 1, c: 2}> // 'a' | 'c'

Let's try to solve this problem within 10 minutes.

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