Problem #3

Problem link
Solution:

package main

func main() {
    target := int64(600851475143)
    arr := make([]bool, 10000)
    prime := 3
    var k int
    for {
        for k = 2 * prime; k < len(arr); k += prime {
            arr[k] = true
        }
        for k = prime + 2; k < len(arr) && arr[k]; k += 2 {
        }
        if k < len(arr) {
            prime = k
            if target%int64(k) == 0 {
                target = target / int64(k)
                if target == 1 {
                    println(k)
                    return
                }
            }
        } else {
            break
            //prevent infinite loop in case the answer
            //is not less than 10000
        }
    }
}

Result: 6857
Time: 0m0.003s