Project Euler 14

14.cpp

#include <iostream>
#include <algorithm>

using namespace::std;

int chainLength(unsigned long long x){
    int len = 1;
    while (x > 1){
        if (x % 2) x = 3*x + 1;
        else x /= 2;
        len++;
    }
    return len;
}

// Max to count to.
int longestChain(unsigned long long x){
    int length =  0;
    int temp;
    int index =0 ;
    for (unsigned long long i = x; i > 0; i-- ){
            temp = chainLength(i);
            if (temp > length){
                length = temp;
                index = i;
            }
    }
    return index;
}

void printCollatz(int x){
    cout << x;
    while (x > 1){
        if (x % 2){
            x = 3*x + 1;
            cout << " --> " << x;
        }
        else {
            x /= 2;
            cout << " --> " << x;
        }
    }
}

int main(void){
    int index = 0;
    unsigned long long x = 1000000;
    int longest = longestChain(x);
    cout << longest << " has the longest chain for numbers less than " << x;
    cout << "\nThat chain is " << chainLength(longest) << " long.";
}