Our team architect has asked us this question which is said to be an interview question from Microsoft long time ago:
Please implement one function which accepts two integers as input and generate the following result accordingly:
If a > b, return 1,
if a = b, return 0,
if a < b, return -1For simplification reason here we can just consider unsigned int ( that is, all importing parameter of integers are greater than or equal to 0 ).
Inside the implementation, you are NOT allowed to use +, -, *, /, > and < for comparison.
There must be multiple ways to achieve it, here below is just one among them. Even we are not allowed to use four arithmetic operations and > or <, we can still leverage the bit operation supported on Integer.
The basic idea is, say we have 6 and 5 for comparison.
Binary format of 6: 0110
Binary format of 5: 0101If we can generate the biggest-sub-bits-series which differentiate the two integers, in the example above it is 0010( since the third bit of both integer are equal ), then we can simply know which is bigger by making bit AND operation:
0110 & 0010 = 10 which <> 0.
0101 & 0010 = 0So we can know 0110 > 0101.
Another example – compare 4 and 3Binary format of 4: 0100
Binary format of 3: 0011The biggest-sub-bits-series: 01000100 & 0100 = 0100 which <> 0
0011 & 0100 = 0So 0100 > 0011.
Solution in JavaScriptfunction compare(a,b){
var diff = a ^ b;
if( diff == 0)
return 0;
diff = diff | ( diff >> 1 );
diff |= diff >> 2;
diff |= diff >> 4;
diff |= diff >> 8;
diff |= diff >> 16;
diff ^= diff >> 1;
return ( a & diff )? 1:-1;
}
console.log(compare(1,2));
console.log(compare(3,2));
console.log(compare(300,2));
console.log(compare(3000,2));
console.log(compare(3000,3000));
console.log(compare(3000,3001));Output:
Solution in Javapublic static int compare(int a, int b){
int diff = a ^ b;
if( diff == 0)
return 0;
diff = diff | ( diff >> 1 );
diff |= diff >> 2;
diff |= diff >> 4;
diff |= diff >> 8;
diff |= diff >> 16;
diff ^= diff >> 1;
return ( (a & diff) == 0 ) ? -1 : 1;
}
System.out.println(compare(1,2));
System.out.println(compare(3,2));
System.out.println(compare(300,2));
System.out.println(compare(3000,2));
System.out.println(compare(3000,3000));
System.out.println(compare(3000,3001));Output:
Solution in ABAP
Since it is not possible to directly perform bit operation on integer in ABAP, in my blog Bitwise operation ( OR, AND, XOR ) on ABAP Integer I simulate these three operations with the help of ABAP internal table. Still it is not enough, the bit shift operation like >> and << are also required to finish this exercise, so I make further enhancement, adding two new methods SHIFT_RIGHT and SHIFT_LEFT in ZCL_INTEGER, which could be found from my github.
Now all prerequisite to finish it using ABAP are fulfilled.
Here it is:
Source code:METHOD compare.
DEFINE shift_right.
lv_diff = a->get_raw_value( ).
a->shift_right( &1 ).
lo_diff = zcl_integer=>value_of( lv_diff ).
a = lo_diff->or( a ).
END-OF-DEFINITION.
DATA(a) = zcl_integer=>value_of( iv_a ).
DATA(b) = zcl_integer=>value_of( iv_b ).
DATA: lv_diff TYPE int4,
lo_diff TYPE REF TO zcl_integer.
a = a->xor( b ).
IF a->get_raw_value( ) IS INITIAL.
rv_result = 0.
RETURN.
ENDIF.
shift_right 1.
shift_right 2.
shift_right 4.
shift_right 8.
shift_right 16.
lv_diff = a->get_raw_value( ).
a->shift_right( 1 ).
lo_diff = zcl_integer=>value_of( lv_diff ).
a = lo_diff->xor( a ).
DATA(lo_origin_a) = zcl_integer=>value_of( iv_a ).
rv_result = zcl_integer=>value_of( lo_origin_a->and( a )->get_raw_value( ) )->get_raw_value( ).
rv_result = COND #( WHEN rv_result IS INITIAL THEN -1 ELSE 1 ).
ENDMETHOD.Test code:WRITE:/ zcl_comparator=>compare( iv_a = 1 iv_B = 2 ).
WRITE:/ zcl_comparator=>compare( iv_a = 3 iv_B = 2 ).
WRITE:/ zcl_comparator=>compare( iv_a = 300 iv_B = 2 ).
WRITE:/ zcl_comparator=>compare( iv_a = 3000 iv_B = 2 ).
WRITE:/ zcl_comparator=>compare( iv_a = 3000 iv_B = 3000 ).
WRITE:/ zcl_comparator=>compare( iv_a = 3000 iv_B = 3001 ).Test output:
Further reading
I have written a series of blogs which compare the language feature among ABAP, JavaScript and Java. You can find a list of them below:
Lazy Loading, Singleton and Bridge design pattern in JavaScript and in ABAP
Functional programming – Simulate Curry in ABAP
Functional Programming – Try Reduce in JavaScript and in ABAP
Simulate Mockito in ABAP
A simulation of Java Spring dependency injection annotation @Inject in ABAP
Singleton bypass – ABAP and Java
Weak reference in ABAP and Java
Fibonacci Sequence in ES5, ES6 and ABAP
Java byte code and ABAP Load
How to write a correct program rejected by compiler: Exception handling in Java and in ABAP
An small example to learn Garbage collection in Java and in ABAP
String Template in ABAP, ES6, Angular and React
Try to access static private attribute via ABAP RTTI and Java Reflection
Local class in ABAP, Java and JavaScript
Integer in ABAP, Java and JavaScript
Covariance in Java and simulation in ABAP
Various Proxy Design Pattern implementation variants in Java and ABAP
Tag(Marker) Interface in ABAP and Java
Bitwise operation ( OR, AND, XOR ) on ABAP Integer
An interview question: Compare two integers without +,-,*,/ or > and <
