LASTDIG - The last digit

Nestor was doing the work of his math class about three days but he is tired of make operations a lot and he should deliver his task tomorrow. His math’s teacher gives him two numbers a and b. The problem consist of finding the last digit of the potency of base a and index b. Help Nestor with his problem. You are given two integer numbers: the base a (0 <= a <= 20) and the index b (0 <= b <= 2,147,483,000), a and b both are not 0. You have to find the last digit of ab.


The first line of input contains an integer t, the number of test cases (t <= 30). t test cases follow. For each test case will appear a and b separated by space.


For each test case output an integer per line representing the result.


3 10
6 2

Output: 9 6

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wolv_dhoni: 2018-04-10 07:41:19

It can be solved in O(1), all you have to do is calculate the last digit of a, a^2, a^3, a^4, after that it just keeps on repeating, you can check it on your own.

flyer2403: 2018-03-22 16:40:33

Last edit: 2018-03-22 16:41:21
jmr99: 2018-03-11 10:32:34

ac in 2 go !! gys use string and consider 700 b limitation.

badasshackme: 2018-03-10 15:21:52

700 B limit is annoying.

venkat016: 2018-01-10 22:31:21

Modular exponenention _/\_ thanks for @ajayc1007 and @prasad_235

vaibhavcs99: 2017-12-31 08:16:40

AC after two TLE (I was using pow function).Modular exponention does the work.No need to consider when one of them is 0 cases.

jaykay12: 2017-12-30 20:57:42


Last edit: 2017-12-30 21:02:13
mayank1208_: 2017-12-30 10:54:11

solved after 5 WA.but got AC in d end....

sgarg367: 2017-12-03 19:07:48

Last edit: 2017-12-03 19:40:13
justinegeo96: 2017-11-25 13:50:18

should i check for negative values for a and b? Why am I getting WA :/ I am getting correct output using fast modular exponentiation.

Added by:Jose Daniel Rodriguez Morales
Time limit:1s
Source limit:700B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Languages:All except: GOSU