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    <p>Yes, there are plenty of times I would not use recursion. Recursion is <em>not</em> free, it has a cost in stack space and that can often be a much more limited resource than some others. There's also a time cost, however small, in setting up and tearing down stack frames.</p> <p>By way of example, the much vaunted factorial function is one where I would probably opt for an iterative approach where the numbers were large. Calculating 10000! with:</p> <pre><code>def factorial (n): if n = 1 return 1 return n * factorial (n-1) </code></pre> <p>will use 10,000 stack frames (assuming it's not optimised by the compiler into an iterative solution of course), quite a lot. The iterative solution:</p> <pre><code>def factorial (n) r = 1 while n &gt; 1: r = r * n n = n - 1 return r </code></pre> <p>will use just the one stack frame and precious little else.</p> <p>It's true that recursive solutions are often more elegant code but you have to temper that with the limitations of your environment.</p> <p>Your <code>carbon</code> example is one where I would actually use recursion since:</p> <ul> <li>it uses at most six stack frames (one per character in the string); and</li> <li>it's relatively elegant, at least much more so than six nested loops and huge equality checks.</li> </ul> <p>For example the following Python code does the trick:</p> <pre><code>def recur (str, pref = ""): # Terminating condition. if str == "": print pref return # Rotate string so all letters get a chance to be first. for i in range (len (str)): recur (str[1:], pref + str[:1]) str = str[1:] + str[:1] recur ("abc") </code></pre> <p>producing:</p> <pre><code>abc acb bca bac cab cba </code></pre> <p>Of course, if your string can be 10K long, I'd rethink it, since that would involve a lot more stack levels but, provided you keep in low enough, recursion is a viable solution.</p>
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    1. POis there ever a time you would not use recursion?
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    1. COTail recursion is as effective as a recursion free version. And in that particular case, recursion is the most adequate solution.
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    2. CO@Nicolas, that's true only if it's actually optimised. Tail-end recursion can be but sometimes the decisions on when to recurse are more complex.
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