Divisors: An integer that can divide another integer without a remainder.
- Finding divisors by dividing all numbers
Condition: Add the number if the remainder is 0 when divided.
Skip if the condition is not met.
Range of condition: The divisor can be at most the number itself, so set the loop to iterate up to the number.
let num = 8; // 약수를 찾기 위한 정수 설정
let result = []
let index = 1;
while (index <= num) {
if (num % index === 0) result.push(index)
index++
}
console.log(result) // [ 1, 2, 4, 8 ]
- Checking only up to half of the given number
Divisors, except for the number itself, cannot be larger than num / 2, so check only up to half.
let num = 8;
let result = []
let index = 1;
while (index <= num / 2) {
if (num % index === 0) result.push(index)
index++
}
result = [...result, num] // 본인 값 추가까지 추가
console.log(result) // [ 1, 2, 4, 8 ]
- Using the square root (Math.sqrt)
Find the divisors of num within the range of 1 to the square root of num.
If num is 100, divide by numbers from 1 to 10 and find those that result in a remainder of 0.
[1, 2, 4, 5, 10]
Also, the result of dividing num by these divisors will be divisors of num.
100 / 1 = 100
100 / 2 = 50
100 / 4 = 25
100 / 5 = 20
100 / 10 = 10 → duplicate
[1, 2, 4, 5, 10, 10, 20, 25, 50, 100]
Remove duplicates
Exclude the divisor from the result if it equals num / divisor.
[1, 2, 4, 5, 10, 20, 25, 50, 100]
Using Set
let num = 100;
let result = []
let index = 1;
while (index <= Math.sqrt(num)) {
if (num % index === 0) {
result.push(index)
if (num / index !== index) result.push(num / index)
}
index++
}
result.sort((a, b) => a - b)
console.log(result) // [ 1, 2, 4, 5, 10, 20, 25, 50, 100 ]
Reference