Collatz

public class CollatzProblem {

    public static void main(String[] args) {
        // This is the number the program will go up to, so to find maximum from 1 to 100, we make k = 100
        int k = 1000000;
        // An array to keep track of the values we get
        int[] length = new int[k];

        // Loop through all possible starting values, from 1 to 'k'
        for(int start = 1; start < k; ++start){
            int current = start;
            int count = 0;

            // This is where iteration happens, we keep iterating until we get a '1'
            // While doing so it counts each iteration
            while(current != 1){
                current = iterate(current); // See next method to see how it iterates
                ++count;
            }

            length[start] = count;

        }
        // This will find the actual maximum value in the array
        int max = length[0];

        for(int i=0; i< k; ++i){
            if(max < length[i]){
                max = length[i];
            }
        }
        // This will find the value that belongs to this 'max', this is the value we want
        int maxIndex = 0;

        for(int i=0; i<k; ++i){
            if(max == length[i]){
                maxIndex = i;
            }
        }

        System.out.println("Index: " + maxIndex + " Amount: " + max);

    }

    public static int iterate(int n){
        // Do as the function says, if n is even, halve it, if n is odd, 3*n+1 is output
        int out = 0;

        if(n%2 == 0){
            out = n/2;
        }
        if(n%2 != 0){
            out = 3*n+1;
        }
        return out;
    }

}