hi kosuke,
lemme give u a hint..
u know how to swap variables without a temp variable?
a, b r the ints..
a=aXORb
b=bXORa (b XOR (a XOR b)) = a
a=aXORb ((a XOR b) XOR a) = b !
if strlen is n then every 'i'th character goes to (n-i) position?
hth,
shail