Chap 7 pg 628 from kathy & Sierra

[aslika bahini]

Hi There,

Given a properly prepared String array containing five elements, which range of results could a proper invocation of Arrays.binarySearch() produce?

A. 0 through 4
B. 0 through 5
C. -1 through 4
D. -1 through 5
E. -5 through 4
F. -5 through 5
G. -6 through 4
H. -6 through 5

The answer is G

I am not able to understand the answer. Can any of you please explain?

Thanks
Saritha

[Sandhya Bhaskara]

Match not found "A" "C" "E" "F" "G" "H"
Insert element
at index -1 -2 -3 -4 -5 -6

Array elements "B" "D" "F" "H" "J"

Match found 0 1 2 3 4


Consider that an array has the strings "B","D","F","H","J", . If match is found he binarySearch method returns the index of match. So it can return values from 0 to 4 if match is found

If match is not found it will return the index where the element could have been inserted
Eg:"A" is not in the array but the correct index where "A" can be inserted is 0. Since 0 is already valid it will return -1.
Similarly for "C" it would return -2 since "C" should go between B and D(0 and 1 index)
"K" would be inserted after "J" and hence -6(See above).
Basically we can insert an element that is not found either at the begining of array or end of the array or inbetween the array elements.

[Sandhya Bhaskara]

Match not found    "A"       "C"      "E"       "F"      "G"      "H"
Insert element
at index           -1        -2       -3        -4       -5      -6
 
Array elements           "B"     "D"       "F"      "H"      "J"
 
Match found               0       1         2        3       4
 

[Ankit Garg]

remember that if a match is not found, binarySearch returns 1's complement of the place where the element should be inserted.

So if the element should be inserted at index 0, it will return -1(1's complement of 0 is -1). Similar is the case for all the indexes.

If you take 1's complement of the negative value that it returns, you will get the index of the location where the element must be inserted. So 1's complement of -1 is 0....

[Rekha Srinath]

To give you a formula for this, the value returned in case of unsuccessful searches will be (-insertionpoint-1), where "insertionpoint" is the zero-based index location where the element could have been inserted.
Taken from: Pg #577, K&B-310-065.

So, for an array of 5 elements, the index locations are from 0 to 4. Hence, on the other end, a new element can be inserted at index 5. As per the formula, the method returns (-5-1) which is -6.

So, the range of values is -6 till 4
[ October 10, 2008: Message edited by: Rekha Srinath ]

[Christophe Verré]

(Just ignore this. I can't resist mentioning that "kathy & Sierra" in the thread title is the same person )

[aslika bahini]

Thanks to all. It helped a lot.

Saritha