asked on

fount 9's in java challenge

Hi,

I am working on below challenge.

I wrote as below

public class Test26 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] nums={1,9,1,9,4};
		System.out.println("return value boolean is--->"+arrayFront9(nums));

	}
	public static boolean arrayFront9(int[] nums) {
		int count=0;
		  for(int num: nums){
		  if(num==9)
			  count++;
		  }
		  
		  if(count>=4)
		  return true;
		
	 /*if(count<4)
		return false;*/
	return false;
	}


}

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I am failing in one test case as below

Expected      Run
arrayFront9({1, 2, 9, 3, 4}) → true      true      OK
arrayFront9({1, 2, 3, 4, 9}) → false      true      X
arrayFront9({1, 2, 3, 4, 5}) → false      false      OK
arrayFront9({9, 2, 3}) → true      true      OK
arrayFront9({1, 9, 9}) → true      true      OK
arrayFront9({1, 2, 3}) → false      false      OK
arrayFront9({1, 9}) → true      true      OK
arrayFront9({5, 5}) → false      false      OK
arrayFront9({2}) → false      false      OK
arrayFront9({9}) → true      true      OK
arrayFront9({}) → false      false      OK
arrayFront9({3, 9, 2, 3, 3}) → true      true      OK
Correct for more than half the tests

How do i fix and improve my program. please advise

dpearson

Your code is counting the number of 9s.

The problem is to see if there is a 9 in the first 4 values.

Can you see how I changed your method and why this works?

	public boolean arrayFront9(int[] nums) {
		int count=0;
		  for(int num: nums){
                    count++ ;
                    
		  if(num==9 && count <= 4)
                     return true ;
		  }
		  
	return false;
	}

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gudii9

ASKER

count++ ;

this counts number of elements in nums array right?

if(num==9 && count <= 4

above statement it will make sure it will check till 4th position only not beyond that and also value is 9 right?

dpearson

Yep that's all correct.

ozo

Can you post a link to this challenge?

dpearson

It's this one:
http://codingbat.com/prob/p186031

Doug

ozo

The method of http:#a40425004 does work for that, but it may be worth noting that if you have a very long array, it could do a lot more work than it needs to before returning false.

I also notice that the code in the original question fails in more than just the one case.

gudii9

ASKER

The method of http:#a40425004 does work for that, but it may be worth noting that if you have a very long array, it could do a lot more work than it needs to before returning false.

Is there is a way to improve it? please advise

The method of http:#a40425004 does work for that, but it may be worth noting that if you have a very long array, it could do a lot more work than it needs to before returning false.

correct it fails for all arrays having 9's having bigger count than 4

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dpearson

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SOLUTION

ozo

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gudii9

ASKER

count < nums.length && count < 4

I see 2 separate conditions clubbed together with &&.

How many number of conditions we can club together?

I was thinking we should say instead as below
count < nums.length && count < =4
Please advise

gudii9

ASKER

You might change
              if(num==9 && count <= 4)
                     return true ;
to
              if(num==9 )
                     return true ;
                  if( count==4 )
                     return false;

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we are still checking all the elements in for each loop and do above step right. How it is going to be different. please advise

dpearson

count < nums.length && count < =4

If you start the loop with "count = 0" you want "count < 4" to do 4 loops.
If you start the loop with "count = 1" you want "count <= 4" to do 4 loops.

We usually loop with counts that start from 0 in the software business, because arrays start from index 0, so you can just do:
int num = nums[count] ;
if the count starts with 0.

You might change
if(num==9 && count <= 4)
return true ;
to
if(num==9 )
return true ;
if( count==4 )
return false;

Yes that's another way to do it.

Doug

gudii9

ASKER

You might change
              if(num==9 && count <= 4)
                     return true ;
to
              if(num==9 )
                     return true ;
                  if( count==4 )
                     return false;

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do you mean it should be like below(within foreach loop? Please advise

public boolean arrayFront9(int[] nums) {
            int count=0;
              for(int num: nums){
count++ ;

       if(num==9 )
return true ;
if( count==4 )
return false;
              }

      return false;
      }

dpearson

Yes that's what ozo is suggesting.

Doug

gudii9

ASKER

what would be the difference. To me both approaches looks same.please advise.

ozo

The difference between http:#a40426848 and http:#a40427058 would be mainly which style of for loop you prefer.
In this case, since you do need the count index, and don't always scan all elements of the array, I might be more inclined to use http:#a40426848, but other preferences can be equally valid.

gudii9

ASKER

In this case, since you do need the count index, and don't always scan all elements of the array

which case you are referring http:#a40426848 or http:#a40427058

in http:#a40427058 scanning of all elements happening in the below lines right?

for(int num: nums){
count++ ;
as given in the complete code below

public boolean arrayFront9(int[] nums) {
            int count=0;
              for(int num: nums){
                    count++ ;
                    
       if(num==9 )
                     return true ;
                  if( count==4 )
                     return false;
              }
              
      return false;
      }

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ozo

The case I am referring to is the problem presented by http://codingbat.com/prob/p186031

In http:#a40427058, scanning of all elements is limited by
if( count==4 )
return false;

dpearson

what would be the difference. To me both approaches looks same.please advise.

They're both logically equivalent since they both solve the problem.

So in that case you generally want the simpler solution, which is usually the one using less lines of code (although not always). So in this situation I'd prefer:

	public boolean arrayFront9(int[] nums) {
                 for (int count = 0 ; count < nums.length && count < 4 ; count++) {
                    int num = nums[count];
		    if(num==9)
                       return true ;
		  }
		  
	         return false;
	}

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It also reads a little easier - because this line:

for (int count = 0 ; count < nums.length && count < 4 ; count++) {

explicitly indicates that we're looping through at most 4 elements of the array, which is otherwise something you only discover later while reading the method (in the alternative solutions, this test for count == 4 comes later).

But at this point it's mostly about a sense of whichever you find clearer. There are no hard and fast rules and really to be a good developer the key is seeing that there are different ways to solve any given problem - so you can weigh the pros and cons of each option.

Doug

gudii9

ASKER

	public boolean arrayFront9(int[] nums) {
                 for (int count = 0 ; count < nums.length && count < 4 ; count++) {
                    int num = nums[count];
		    if(num==9)
                       return true ;
		  }
		  
	         return false;
	}

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I too feel above code is more readable and simple.Rather than checking inside for loop by putting separate if condition to see if count==4 as below

if(num==9 )
return true ;
if( count==4 )
return false;

gudii9

ASKER

Can you see why it makes sense here to use the older style (for int i = 0 ; i < ... ; i++) style of loop here?

i finally got using old for loop rather than new for each loop is advisable in this case to avoid scanning elements beyond count 4 right. please advise