isEverywhere  challenge

gudii9
gudii9 used Ask the Experts™
on
Hi,

I am working on below challenge

http://codingbat.com/prob/p110222

Psedo code description of approach :
1. loop through array
2.check every adjacent values has given val
3. if yes return true
4. if no return false





I am not passing all tests
Expected      Run            
isEverywhere([1, 2, 1, 3], 1) → true      true      OK      
isEverywhere([1, 2, 1, 3], 2) → false      true      X      
isEverywhere([1, 2, 1, 3, 4], 1) → false      true      X      
isEverywhere([2, 1, 2, 1], 1) → true      true      OK      
isEverywhere([2, 1, 2, 1], 2) → true      true      OK      
isEverywhere([2, 1, 2, 3, 1], 2) → false      true      X      
isEverywhere([3, 1], 3) → true      true      OK      
isEverywhere([3, 1], 2) → false      false      OK      
isEverywhere([3], 1) → true      false      X      
isEverywhere([], 1) → true      false      X      
isEverywhere([1, 2, 1, 2, 3, 2, 5], 2) → true      true      OK      
isEverywhere([1, 2, 1, 1, 1, 2], 2) → false      true      X      
isEverywhere([2, 1, 2, 1, 1, 2], 2) → false      true      X      
isEverywhere([2, 1, 2, 2, 2, 1, 1, 2], 2) → false      true      X      
isEverywhere([2, 1, 2, 2, 2, 1, 2, 1], 2) → true      true      OK      
isEverywhere([2, 1, 2, 1, 2], 2) → true      true      OK      
other tests
X      

How to improve my design, approach, code? please advise
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Top Expert 2016

Commented:
Their tests are wrong. e.g.

isEverywhere([2, 1, 2, 1, 1, 2], 2) → false	true	X	

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Author

Commented:
public boolean isEverywhere(int[] nums, int val) {
boolean result = false;
for (int i = 0; i <=nums.length-2;i++)
{
if ( nums[i] == val && nums[i+1] == val)
result = true;
}
  return result;
}

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is my code is correct? any modifications i can do to this. I am having hard time with edge cases? any tips to be 100% right on edge cases all the time?
CPColinSenior Java Architect

Commented:
Their tests are wrong. e.g.

How so? That array has two 1's next to each other, so it should fail.

is my code is correct?

Looks like you're checking to see if both elements equal the value. Is that what you want?

Author

Commented:
We'll say that a value is "everywhere" in an array if for every pair of adjacent elements in the array, at least one of the pair is that value. Return true if the given value is everywhere in the array.

isEverywhere([1, 2, 1, 3], 1) → true
isEverywhere([1, 2, 1, 3], 2) → false
isEverywhere([1, 2, 1, 3, 4], 1) → false

Is that what you want?

that is what i understood from above challenge. i could be wrong?
CPColinSenior Java Architect

Commented:
Think carefully about when that if statement will return true and when it will return false. Will it return true if you pass it [1, 1]? How about [1, 2]?
Top Expert 2016

Commented:
How so? That array has two 1's next to each other, so it should fail.
Ah - i think i was misinterpreting the question. I thought they meant distinct pairs with no overlaps
Amusingly the problem is much easier when you don't take the path i did ;)

Author

Commented:
Will it return true if you pass it [1, 1]? How about [1, 2]?

i have not get this. method needs two arguments right? what is second argument?

  isEverywhere([1, 1],1)  is true
How about isEverywhere([1, 2], 1)  is false
How about isEverywhere([1, 2], 2) also false?
CPColinSenior Java Architect
Commented:
Here's one of the tests:

isEverywhere([3, 1], 3) → true

What will your if statement do in this situation?

(This is what I mean, by the way, when I suggest that you break down the problem into small pieces. This is a test you're failing; focus on understanding why.)

Author

Commented:
it is again looks like edge case issue

Author

Commented:
isEverywhere([3, 1], 3) → true

What will your if statement do in this situation?

(This is what I mean, by the way, when I suggest that you break down the problem into small pieces. This is a test you're failing; focus on understanding why.)

i stretching further in my thinking in terms of logic around this

Author

Commented:
public boolean isEverywhere(int[] nums, int val) {
boolean result = false;
for (int i = 0; i <=nums.length-2;i++)
{
if ( nums[i] == val || nums[i+1] == val)
result = true;
}
  return result;
}

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above fails below when i replace || with &&


Correct for more than half the tests

Your progress graph for this problem


i am confused mainly in 2 things

1. edge cases
2. usage of || and && since some experts used && for OR description of challenge and vice versa. How to know what to use?
CPColinSenior Java Architect

Commented:
"Return true if, for every pair, condition X is true." is logically equivalent to "Return false if, for any pair, condition X is false." When you're designing your code, you should use whichever is easier. In this case, you tried it the first way and couldn't get it to work, so it might be time to try it the second way.

Author

Commented:
public boolean isEverywhere(int[] nums, int val) {
boolean result = true;
for (int i = 0; i <=nums.length-2;i++)
{
if ( nums[i] != val || nums[i+1] != val)
result = false;
}
  return result;
}



//"Return true if, for every pair, condition X is true." is logically 
//equivalent to "Return false if, for any pair, condition X is false." 

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above corollary approach failing below tests
Expected      Run            
isEverywhere([1, 2, 1, 3], 1) → true      false      X      
isEverywhere([1, 2, 1, 3], 2) → false      false      OK      
isEverywhere([1, 2, 1, 3, 4], 1) → false      false      OK      
isEverywhere([2, 1, 2, 1], 1) → true      false      X      
isEverywhere([2, 1, 2, 1], 2) → true      false      X      
isEverywhere([2, 1, 2, 3, 1], 2) → false      false      OK      
isEverywhere([3, 1], 3) → true      false      X      
isEverywhere([3, 1], 2) → false      false      OK      
isEverywhere([3], 1) → true      true      OK      
isEverywhere([], 1) → true      true      OK      
isEverywhere([1, 2, 1, 2, 3, 2, 5], 2) → true      false      X      
isEverywhere([1, 2, 1, 1, 1, 2], 2) → false      false      OK      
isEverywhere([2, 1, 2, 1, 1, 2], 2) → false      false      OK      
isEverywhere([2, 1, 2, 2, 2, 1, 1, 2], 2) → false      false      OK      
isEverywhere([2, 1, 2, 2, 2, 1, 2, 1], 2) → true      false      X      
isEverywhere([2, 1, 2, 1, 2], 2) → true      false      X      
other tests
X      
CPColinSenior Java Architect

Commented:
Once again, break it down. Take this test and figure out why your code is failing:

isEverywhere([3, 1], 3) → true

Author

Commented:
public boolean isEverywhere(int[] nums, int val) {
boolean result = false;
for (int i = 0; i <=nums.length-2;i++)
{
if ( nums[i] == val || nums[i+1] == val)
result = true;
i=i+1;
}
  return result;
}



//"Return true if, for every pair, condition X is true." is logically 
//equivalent to "Return false if, for any pair, condition X is false." 

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i fixded above test by taking 100% sure approach which is if 3 is there in {3,1} then it is true 100% of the time irrespective of following pair of elements



if no target value in {3.1} we cannot say 100% as false since following pair of values may have target value so that is bad approach in this case(which happened to be my original approach)

Author

Commented:
isEverywhere([1, 2, 1, 3], 2) → false      true      X

i was not clear why above is expected false.

i thought it should be true as target int 2 is present in first pair

similarly i though below should be true

isEverywhere([1, 2, 1, 3, 4], 1) → false      true      X

Author

Commented:
isEverywhere([1, 2, 1, 3], 2) → false
isEverywhere([1, 2, 1, 3, 4], 1) → false

i thought above 2 also true as per below explanation of challenge
We'll say that a value is "everywhere" in an array if for every pair of adjacent elements in the array, at least one of the pair is that value. Return true if the given value is everywhere in the array.
I guess there is a mistake in the question.

"We'll say that a value is "everywhere" in an array if for every pair of adjacent elements in the array, at least one of the pair is that value. Return true if the given value is everywhere in the array."

It should actually be "We'll say that a value is "everywhere" in an array if for every pair of adjacent elements in the array, at least one of the elements has that value. Return true if the given value is everywhere in the array."

I have underlined the pair that causes the condition to fail.
isEverywhere([1, 2, 1, 3], 2) → false
isEverywhere([1, 2, 1, 3, 4], 1) → false
isEverywhere([1, 2, 1, 3], 2) → false
isEverywhere([1, 2, 1, 3, 4], 1) → false

Author

Commented:
I got it.

corollary or back ward reverse approach works.

psuedocode description of loic is


1. iterate each element
2. check first element and second elemt as not equal to target element then return isEverywhere false 100% sure case
3. else return true case.

public boolean isEverywhere(int[] nums, int val) {
boolean result = true;
for (int i = 0; i <=nums.length-2;i++)
{
if ( nums[i] != val && nums[i+1] != val)
result = false;
}
  return result;
}

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above pass all tests

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