If length of string is 1 or 0
if ( s == null || s . length ( ) <= 1 ) { return s ; } int i = 0 ; while ( i < s . length ( ) ) { if ( i + 1 < s . length ( ) && s . charAt ( i ) == s . charAt ( i + 1 ) ) { int j = i ; while ( j + 1 < s . length ( ) && s . charAt ( j ) == s . charAt ( j + 1 ) ) { j ++ ; } char lastChar = i > 0 ? s . charAt ( i - 1 ) : ch ; String remStr = removeDuplicates ( s . substring ( j + 1 , s . length ( ) ) , lastChar ) ; s = s . substring ( 0 , i ) ; int k = s . length ( ) , l = 0 ;