Daily Challenge 250 - Last Digit of a Large Number

Define a function that takes in two non-negative integers a and b and returns the last decimal digit of a^b. Note that a and b may be very large!

For example, the last decimal digit of 9^7 is 9, since 9^7 = 4782969. The last decimal digit of (2^200)^(2^300), which has over 10^92 decimal digits, is 6. Also, please take 0^0 to be 1.

You may assume that the input will always be valid.

Examples

lastDigit 4 1 shouldBe 4
lastDigit 4 2 shouldBe 6
lastDigit 9 7 shouldBe 9

Tests

lastDigit 10 (10^10)

lastDigit (2^200) (2^300)

This challenge comes from dburgoyne on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

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