One programming question every day ------ program Words in one sentence in reverse order

Baidu company interview questions require minimal space complexity. I hope you can better answer these questions ........................

/*** Requirement: invert an English sentence * but cannot use string library functions: Split, indexof, lastindexof, substring and minimum space complexity ***/public class reverse {public static void main (string [] ARGs) {string STR = "Who am I"; system. out. println (reverse (STR);} public static string reverse (string Str) {int position = 0; int I = 0; stringbuilder sb = new stringbuilder (); while (I <Str. length () {char temp = Str. charat (I); If (temp = '') {position = 0; sb. insert (Position, temp);} else {sb. insert (Position, temp); position ++;} I ++;} return sb. tostring ();}}