question: private String [ ] diff_halfMatchI ( String longtext , String shorttext , int i ) { String seed = longtext . substring ( i , i + longtext . length ( ) / 4 ) ; int j = - 1 ; String best_common = "" ; String best_longtext_a = "" , best_longtext_b = "" ; String best_shorttext_a = "" , best_shorttext_b = "" ; while ( ( j = shorttext . indexOf ( seed , j + 1 ) ) != - 1 ) { int prefixLength = diff_commonPrefix ( longtext . substring ( i ) , shorttext . substring ( j ) ) ; int suffixLength = diff_commonSuffix ( longtext . substring ( 0 , i ) , shorttext . substring ( 0 , j ) ) ; if ( best_common . length ( ) < suffixLength + prefixLength ) { best_common = shorttext . substring ( j - suffixLength , j ) + shorttext . substring ( j , j + prefixLength ) ; best_longtext_a = longtext . substring ( 0 , i - suffixLength ) ; best_longtext_b = longtext . substring ( i + prefixLength ) ; best_shorttext_a = shorttext . substring ( 0 , j - suffixLength ) ; best_shorttext_b = shorttext . substring ( j + prefixLength ) ; } } if ( best_common . length ( ) * 2 >= longtext . length ( ) ) { return new String [ ] { best_longtext_a , best_longtext_b , best_shorttext_a , best_shorttext_b , best_common } ; } else { return null ; } }
target:  Does a substring of shorttext exist within longtext such that the substring is at least half the length of longtext?