Bit of a cheat really .......

0+1+2+3+4+5+6+7+8+9 = 45

Take  0123456789 (sum of which is 45) from 9876543210 (sum of which is also 45)
Answer is 9753086421 (sum of which is also 45)

            9876543210
minus  0123456789
-------------------------
           9753086421