Discovering the highest prime factor of a number using Javascript

Question

Discovering the highest prime factor of a number using Javascript

My current focus is on creating a basic program in JavaScript that can identify the largest prime factor of an integer. Here is the code I have developed for this purpose:

let result;

function findFactor(number, half) {
    for (let i = 2; i < half; i++) {
        if (number % i == 0) {
            result = number / i;
            findFactor(result, result / 2);
        }
    }
}

findFactor(30, 15);
console.log(result);

While the efficiency and accuracy of this code remains uncertain, there is a specific issue that has grabbed my attention: After the i = 2 step within the findFactor function, I noticed that the values of number = 5, half = 2.5, and result = 5. However, without any explicit instruction in the code to make changes, the values suddenly revert back to 15 and 7.5. This unexpected behavior requires further investigation.

javascript

Answer 1

Answer №1

The function is being called recursively, and each time it's called, a new set of variables for target, half, and i is created. For instance, in the initial call to factor, target is 30 and half is 15. When the function is called again with arguments 15 and 7.5, the inner call gets its own sets of target (15) and half (7.5), while the outer call retains its copies of target (30) and half (15). This pattern continues with subsequent recursive calls to factor, creating distinct sets of variables each time. As you return from the innermost call, its variables are cleared out, revealing the values from the calling context.

To illustrate this concept more simply, consider the following example:

function countdown(value, indent) {
    var twice = value * 2;
    console.log(indent + "[before] value = " + value + ", twice = " + twice);
    if (value > 0) {
        countdown(value - 1, indent + "  ");
    }
    console.log(indent + "[after]  value = " + value + ", twice = " + twice);
}
countdown(3, "");

.as-console-wrapper {
    max-height: 100% !important;
}

The output generated by this code snippet is as follows:

[before] value = 3, twice = 6
  [before] value = 2, twice = 4
    [before] value = 1, twice = 2
      [before] value = 0, twice = 0
      [after]  value = 0, twice = 0
    [after]  value = 1, twice = 2
  [after]  value = 2, twice = 4
[after]  value = 3, twice = 6

This output demonstrates that changes made in an inner call do not affect variables in the outer scope; each invocation creates its own separate set of variables.

Answer 2

The function is being called recursively, and each time it's called, a new set of variables for target, half, and i is created. For instance, in the initial call to factor, target is 30 and half is 15. When the function is called again with arguments 15 and 7.5, the inner call gets its own sets of target (15) and half (7.5), while the outer call retains its copies of target (30) and half (15). This pattern continues with subsequent recursive calls to factor, creating distinct sets of variables each time. As you return from the innermost call, its variables are cleared out, revealing the values from the calling context.

To illustrate this concept more simply, consider the following example:

function countdown(value, indent) {
    var twice = value * 2;
    console.log(indent + "[before] value = " + value + ", twice = " + twice);
    if (value > 0) {
        countdown(value - 1, indent + "  ");
    }
    console.log(indent + "[after]  value = " + value + ", twice = " + twice);
}
countdown(3, "");

.as-console-wrapper {
    max-height: 100% !important;
}

The output generated by this code snippet is as follows:

[before] value = 3, twice = 6
  [before] value = 2, twice = 4
    [before] value = 1, twice = 2
      [before] value = 0, twice = 0
      [after]  value = 0, twice = 0
    [after]  value = 1, twice = 2
  [after]  value = 2, twice = 4
[after]  value = 3, twice = 6

This output demonstrates that changes made in an inner call do not affect variables in the outer scope; each invocation creates its own separate set of variables.

Discovering the highest prime factor of a number using Javascript

Answer №1

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