Check if S2 [ 0. . . i ] is a scrambled string of S1 [ 0. . . i ] and if S2 [ i + 1. . . n ] is a scrambled string of S1 [ i + 1. . . n ]
if ( isScramble ( S1 . substring ( 0 , i ) , S2 . substring ( 0 , i ) ) && isScramble ( S1 . substring ( i , n ) , S2 . substring ( i , n ) ) ) { return true ; }