How do you empty a vase containing five flowers? Answer: if the vase is not empty, you take out one flower and then you empty a vase containing four flowers. How do you empty a vase containing four flowers? Answer: if the vase is not empty, you take out one flower and then you empty … Read more
Usually, I replace a recursive algorithm by an iterative algorithm by pushing the parameters that would normally be passed to the recursive function onto a stack. In fact, you are replacing the program stack by one of your own. var stack = []; stack.push(firstObject); // while not empty while (stack.length) { // Pop off end … Read more
Tail-call optimization is where you are able to avoid allocating a new stack frame for a function because the calling function will simply return the value that it gets from the called function. The most common use is tail-recursion, where a recursive function written to take advantage of tail-call optimization can use constant stack space. … Read more
What is tail recursion?
It is a guard against a stack overflow, yes. Python (or rather, the CPython implementation) doesn’t optimize tail recursion, and unbridled recursion causes stack overflows. You can check the recursion limit with sys.getrecursionlimit: import sys print(sys.getrecursionlimit()) and change the recursion limit with sys.setrecursionlimit: sys.setrecursionlimit(1500) but doing so is dangerous — the standard limit is a … Read more
Now that MySQL 8.0 supports recursive queries, we can say that all popular SQL databases support recursive queries in standard syntax. WITH RECURSIVE MyTree AS ( SELECT * FROM MyTable WHERE ParentId IS NULL UNION ALL SELECT m.* FROM MyTABLE AS m JOIN MyTree AS t ON m.ParentId = t.Id ) SELECT * FROM MyTree; … Read more
It is returning None because when you recursively call it: if my_var != “a” and my_var != “b”: print(‘You didn\’t type “a” or “b”. Try again.’) get_input() ..you don’t return the value. So while the recursion does happen, the return value gets discarded, and then you fall off the end of the function. Falling off … Read more
If you’re walking the tree from the root down, you don’t need to propagate ‘counts’ downward at all–the fact that you are is resulting in repeated counting of nodes as they contribute to both count, countLeft, and countRight, since you increment count before passing it to nodesGreaterThanX for the children. public static int nodesGreaterThanX(BinaryTreeNode<Integer> node, … Read more
Your DrowRanger method is calling itself infinitely. This is almost always the cause of a StackOverflowException. This line: return DrowRanger(); Calls the DrowRanger method, but since you’re inside the DrowRanger method it just keeps calling itself infinitely. I think you meant to return the local object: return DrowRanger; In general, it is a bad idea … Read more