Test 3 & 4 failed why

Question

I am solving code coach problem of extra terrestrial
The test 1,2,5 completed
But 3&4 failed I don't know what's the issue
Could u pls help me

https://code.sololearn.com/cu8VHYGsowqH/?ref=app

Answer 1

rev[ j ]='\0'; // not rev[ i ]