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POGetting odd results when trying to solve Collatz p‌r‌o‌b‌l‌e‌m
 

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  1. POGetting odd results when trying to solve Collatz p‌r‌o‌b‌l‌e‌m
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    <p>I'm trying to solving Project Euler <a href="https://projecteuler.net/problem=14" rel="nofollow noreferrer">Problem 14</a>. It asks to find the number under 1 million that generates the longest sequence. What I did was create a vector, v, and populate its elements with the length of the sequence for a particular number. Thus, the element that resides in position 13 will correspond to the length of the sequence generated by the number 13, and so on. However, some seemingly random elements take very large numbers and I can't figure out what's wrong with the code. Also, when I test it with 1,000,000, I get a completely wrong answer, but I know the program is working for some small numbers after testing them by hand and verifying.</p> <pre><code>#include &lt;iostream&gt; #include &lt;vector&gt; using namespace std; void find_longest(int n) { int count = 1; int max = 0; int position; vector&lt;int&gt; v; v.push_back(0); v.push_back(0); for(int i = 1; i &lt; n; i++) { long long int trainer = i; count = 1; while(trainer != 1) { if(trainer%2 == 0) { trainer /= 2; count++; } else { trainer = 3*trainer + 1; count++; } } v.push_back(count); } vector&lt;int&gt;::iterator it; for(it = v.begin(); it &lt; v.end(); it++) { cout &lt;&lt; v[*it] &lt;&lt; endl; //if(v[*it] &gt; max) //{ // max = v[*it]; // position = *it; //} } //cout &lt;&lt; "The longest sequence is " &lt;&lt; max &lt;&lt; " terms long and is "; //cout &lt;&lt; "generated by the number " &lt;&lt; position &lt;&lt; "." &lt;&lt; endl; } int main() { find_longest(100); //find_longest(1000000); } </code></pre>
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    1. USBob John
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    1. COI'm not seeing where you store the overall maximum total. I see "max" at the top of your code, but I never see "count" overwriting "max" if "count" > "max".
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      1. POGetting odd results when trying to solve Collatz p‌r‌o‌b‌l‌e‌m
      1. USInisheer
    2. COisn't `*it` the number? Not `v[*it]`?
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      1. POGetting odd results when trying to solve Collatz p‌r‌o‌b‌l‌e‌m
      1. USJohn Corbett
    3. COAlso, I'm confused why you're storing anything within a vector<>. I believe you should just store "max" and "value" for the starting number that created the longest sequence.
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      1. USInisheer
 

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