Basics of Java : Project Euler problems

Question

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

Find the sum of all the even-valued terms in the sequence which do not exceed four million.

My code:

    int x = 0;
    int y = 1;
    int z;
    int sum = 0;


        for(int i = 0; i <= 4000000; i++)
        {
        z = x + y;
        x = y;
        y = z;
        if(y % 2 == 0)
        {
            sum = sum + y;
        }


    }
    System.out.println(sum);

}

That outputs 1110529254 but, the correct answer is 4613732.

Help would be very much appreciated.

Let me know if the discussion here does not address your problem, but this is what's happening. — chrylis -cautiouslyoptimistic-, Apr 24 '18 at 19:58
You are iterating 4 million times. You are not checking if the number in the sequence exceeds 4 million. — Ivar, Apr 24 '18 at 19:59
*"even-valued **terms** in the sequence which **do not exceed** four million"* means that the Fibonacci *value* should not exceed 4 million, that that you should go through that *many* Fibonacci numbers. — Andreas, Apr 24 '18 at 19:59
@chrylis I don't think the duplicate is on point. See my comment above. — Andreas, Apr 24 '18 at 20:00
You might find this useful: https://codereview.stackexchange.com/questions/77124/project-euler-2-fibonacci-sequence/77174 — Pablo, Apr 24 '18 at 20:01
Indeed, changing the `for` loop to `while (z <= 4000000)` fixes this for me. Note that in C# at least you'll have to initialize `z` to 0. — EJoshuaS - Stand with Ukraine, Apr 24 '18 at 20:02
*Solution:* Replace `for(int i = 0; i <= 4000000; i++)` with `while (y <= 4000000)` — Andreas, Apr 24 '18 at 20:02
@Andreas Yes, I tried something similar and it worked for me. — EJoshuaS - Stand with Ukraine, Apr 24 '18 at 20:04
@Andreas Thank you, my code is now producing the correct result. — Mukarram Waqqas, Apr 24 '18 at 20:07
@Andreas Good call, I didn't parse the problem statement correctly at first. — chrylis -cautiouslyoptimistic-, Apr 24 '18 at 20:07

score 0 · Accepted Answer · answered May 21 '18 at 22:22

Your code does iteration 4 million times but it does not check the sum of all the even-valued terms in the sequence whether do not exceed four million or not.

Below you can find my variant of getting sum of all the even-valued terms in the sequence which dont exceed for million.

 public class Example_1 {
    public static void main(String args[]) {

      int x = 0;
      int y = 1;
      int z;
      int sum = 0;

      while (true) {
          z = x + y;
          x = y;
          y = z;
          if(y % 2 == 0) {
             sum = sum + y;
          }
          if (sum >= 4000000){
              break;
          }
      }
      System.out.println("Sum: " + sum);
  }
}

The answer which I get from this code is 4613732 as we expected.

Basics of Java : Project Euler problems

1 Answers1