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array220 challenge

Posted on 2016-09-21
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Last Modified: 2016-09-22
Hi,
I am working on below challenge and not cclear on description. please advise

http://codingbat.com/prob/p173469


Recursion-1 > array220
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Given an array of ints, compute recursively if the array contains somewhere a value followed in the array by that value times 10. We'll use the convention of considering only the part of the array that begins at the given index. In this way, a recursive call can pass index+1 to move down the array. The initial call will pass in index as 0.

array220([1, 2, 20], 0) → true
array220([3, 30], 0) → true
array220([3], 0) → false
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Question by:gudii9
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Expert Comment

by:sarabande
ID: 41809324
- recursion stops with false if the index is greater or equal to array length.
- if the index is greater than 0 and nums[index] is equal to 10 times nums[index-1] then stop with success.
- proceed recursion by calling array220 passing the array and the index incremented by 1 and return the result.

Sara
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Author Comment

by:gudii9
ID: 41810760
array220([1, 2, 20], 0) → true
array220([3, 30], 0) → true
array220([3], 0) → false

how above is true and true then false?

array220([1, 2, 20], 0) → true

element at 0 index of above array is 1 so 1 *10 is 10 are we expected to see 10 in rest of elements and if found return true else false?
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Accepted Solution

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sarabande earned 500 total points
ID: 41810914
these are 3 different tests and not a sequence of recursive calls

array220([1, 2, 20], 0) → true  because 2 * 10 == 20  (3rd recursive call)

array220([3, 30], 0) → true      because3 * 10 == 30  (2nd recursive call)

array220([3], 0) → false           because the array only has 1 element.

so 1 *10 is 10 are we expected to see 10 in rest of elements

the challenge is to find a pair of consecutive numbers where (left * 10 == right).

so you have to check whether the 1 was followed by 10 and if that is not the case whether you have more luck with the next pair.

Sara
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Author Comment

by:gudii9
ID: 41811159
the challenge is to find a pair of consecutive numbers where (left * 10 == right).

above is clear. let me think
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LVL 7

Author Comment

by:gudii9
ID: 41811180
public boolean array220(int[] nums, int index) {
  if(index>nums.length-2){
    return false;
  }
if(nums[index+1]==nums[index]*10){
  return true;
}
else{
  return array220(nums,index+1);
}

}

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above passed all tests. any improvements or alternate approaches?
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LVL 7

Author Comment

by:gudii9
ID: 41811188
public boolean array220(int[] nums, int index) {
  if(index>nums.length-2){
    return false;
  }
if(nums[index]*10==nums[index+1]){
  return true;
}
else{
  return array220(nums,index+1);
}

}


/*- recursion stops with false if the index is greater or equal to array length.
- if the index is greater than 0 and nums[index] is equal to 10 times nums[index-1] 
then stop with success.
- proceed recursion by calling array220 passing the array and the index incremented 
by 1 and return the result.
*/

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above bit refined i think
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LVL 33

Expert Comment

by:sarabande
ID: 41811244
any improvements or alternate approaches?

the 'index>nums.length-2' looks a little bit clumsy.

normally, if a range of indices needs to be handled i prefer to skip the index 0 and then can use nums[index-1] and nums[index].

public boolean array220(int[] nums, int index) {
  if(index>=nums.length){
    return false;
  }
if(index > 0 && nums[index-1]*10==nums[index]){
  return true;
}
return array220(nums,index+1);

}

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Sara
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LVL 7

Author Comment

by:gudii9
ID: 41811284
sure. got it
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