What is inverse function to XOR?

The inverse is XOR!

If you have:

c = a^b;

You can get a or b back if you have the other value available:

a = c^b; // or b^c (order is not important)
b = c^a; // or a^c

For example if a = 5, b = 3 (and thus c = 6 as you mentioned) you get:

b=0011 (3)            a=0101 (5)
c=0110 (6) XOR   or   c=0110 (6) XOR
----------            ----------
a=0101 (5)            b=0011 (3)

The inverse of XOR is XOR itself.
I came across a similar problem on leetcode. Leetcode-1720

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