What Is the 10001St Prime Number? Why Does My Java Solution Give the Error Arrayindexoutofboundsexception?
So This Is My Java Code for Project Euler #7(Description of Problem Commented out in Code): // by Listing the First Six Prime Numbers: 2, 3, 5, 7, 11, and 13...
So this is my Java code for Project Euler #7(description of problem commented out in code):
// By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
// What is the 10001st prime number?
boolean isPrime = true;
long [] primes = new long[10001];
int j = 0;
while (j < 10001){
for (long i = 2; i < 1000000000000000L; i++) {
for (long k = i; k < i / 2; k++) {
if (i % k == 0) {
isPrime = false;
break;
}
}
if (isPrime) {
primes[j] = i;
j++;
}
}
}
System.out.println(primes[10000]);
When I run this code, this is what I get as a result :
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10001
*at vasila.mir.Main.main(Main.java from InputFileObject:22)*
When I press on the ArrayIndexOutOfBoundsException error it gives me this "Find why 'j' could be 10001". When I press on that, this is what I get :
primes[j] = i; in Main.main(String[]) (filter: 10001)
I don't understand what that means, and it doesn't really help me. What could be the problem with my code?
1 Answer
If your for (long i = 2; i < 1000000000000000L; i++) finds more that 10001 primes, your outer loops condition is never checked in time to finish the program.
You should combine the loops
Change
while (j < 10001){
for (long i = 2; i < 1000000000000000L; i++) {
to
for (long i = 2; i < 1000000000000000L && j < 10001; i++) {
You should also reset isPrime to true at the start of the outer for loop.
And in the inner loop, k should start at 2, not i.
The following works:
long [] primes = new long[10001];
int j = 0;
for (long i = 2; i < 1000000000000000L && j < 10001; i++) {
boolean isPrime = true;
for (long k = 2; k <= i / 2; k++) {
if (i % k == 0) {
isPrime = false;
break;
}
}
if (isPrime) {
primes[j] = i;
j++;
}
}
System.out.println(primes[10000]);
Output:
104743
Sarah Jenkins is a veteran tech journalist with over 12 years of experience covering artificial intelligence, mobile innovations, and digital ethics. Her insights have appeared in leading technology publications worldwide.
