Initial commit

.gitignore

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+# Ignore emacs backups
+*~
+
+# Ignore build
+collatz*

Makefile

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+default:
+	g++ main.cpp -o collatz

README.md

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+# Collatz conjecture solver
+### (x%2==0) ? x/=2 : x=x*3+1;
+
+Program to solver the (Collatz conjecture)[https://en.wikipedia.org/wiki/Collatz_conjecture].
+
+Algorithm:
+- Start with number.
+- If number is even, divide by two.
+- If number is odd, multiply by three and add one.
+- Repeat.
+
+To figure out if it will repeat, save all the previous numbers, and check if the current number is one of those.
+If it is, that means it will repeat, and you have disproved the Collatz conjecture. So far, though, nobody has disproven it up to 2^68.

main.cpp

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+#include <iostream>
+#include <string>
+
+// TODO:
+//  Use GMP for numbers (to allow for really big numbers)
+//  Make disproving mode
+//  Make no print mode (for speed, implement after disproving mode)
+
+int main(int argc, char* argv[]) {
+  // If number not provided
+  if (argc < 2) {
+    std::cout << "Usage: " << argv[0] << " <number>\n";
+    exit(1);
+  }
+  long long x { std::stoll(argv[1]) };
+  std::cout << x << '\n';
+  while (x != 1) {
+    if (x % 2 == 0)
+      x /= 2;
+    else if (x % 2)
+      x = x*3+1;
+    std::cout << x << '\n';
+  }
+}