# "Drop It" algorithm issues

My algorithm below passes on every test except for

dropElements([1, 2, 3, 4], function(n) {return n > 5;});

in which the output is [3, 4]. Could anyone tell me why my algorithm isn’t returning [], but [3,4] instead?

``````function dropElements(arr, funct) {

for(i=0; i <arr.length; ++i){

if(funct(arr) === false){

arr.shift();
}
else if(funct(arr) === true){
return arr;
}
}

return arr;
}
``````

you are modifying the array in the loop you are iterating. so it drops the first 2 elements and then its at then end of the array and returns. It is seldom do you actually want to delete elements from an array in a loop that you are iterating over.

you are also modifying the array that was passed to you.

try using a temporary array in the function and returning that.

Your algorithm may pass most of the provided tests but there are two critical errors that makes your algorithm incorrect: 1) you are mutating the array while iterating on the same array, 2) you are returning the array as soon as the condition is met.

1. you are mutating the array while iterating over the same array.

To see why this is problematic, keep track on variables affected by each iteration.
Iteration #1

``````arr.length = 4
i = 0
``````

Iteration #2

``````arr.length = 3
i = 1
``````

Iteration #3

``````arr.length = 2
i = 2
``````

Based on your loop condition, iteration ends here and returns the array, [3, 4]

1. you are returning the array as soon as the condition is met.
Consider following,
``````// Drop element that doesn't meet the requirement specified by callback function.
dropElements([3, 2, 1], function(n) {
return n  > 2;
});

// Expects: [ 3 ]
// Yields: [3, 2, 1]
``````

On first iteration, since 3 is greater than 2, the code flows to return statement in ‘else-if’ clause that will terminate the loop. Hence, your algorithm yields incorrect result, [3, 2, 1].

Hi,
I could pass it but I’m afraid that it’s not an ideal code…

``````function dropElements(arr,func) {
for (var i =0; i<arr.length+i; i++) {
if(func(arr) === false ) {
arr.shift();
} else {
return arr;
}
}
return arr;
}

dropElements([1, 2, 3, 4], function(n) {return n > 5;});``````