Leecode-268. missing numbers (Application of XOR, find numbers that do not appear, find numbers that only appear once)

Look for numbers that don't appear 、 Find the first number that appears , Are classic applications of XOR

Operation symbol ：^

Operational rules ： Same as 0 different 1

Law of satisfaction ： Associative law ：a^b^c=a^(b^c);

                The law of reflexion ：a^a=0;

                Law of identity ：a^0=a;

Only the number to be found appears once in the array , All other numbers appear twice . From the above three rules , XOR all numbers , Finally, get the number that only appears once