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Commit 240dfc3

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Added Recursion Topic
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public class Recursion {
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// Used Example Of Factorial
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public class Factorial {
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public int recursiveFactorial(int n) {
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if (n > 0) {
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System.out.println("Execution of: " + n);
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return n * recursiveFactorial(n - 1);
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} else {
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return 1;
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}
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}
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public void main(String[] args) {
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int recursiveSolution = recursiveFactorial(4);
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System.out.println(recursiveSolution);
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}
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}
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}
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# Recursion
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Recursion has _two_ fundamental aspects:
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1. **Base Case**
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2. **Recursive Step**
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When using iteration, we rely on a counting variable and a boolean condition.
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For example, when iterating through the values in a list, we would increment the counting variable until it exceeded the length of the dataset.
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Recursive functions have a similar concept, which we call the **base case**.
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The _base case_ dictates whether the function will recurse, or call itself. Without a base case, it’s the iterative equivalent to writing an _infinite loop_.
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Because we’re using a **call stack** to track the function calls, your computer will throw an error due to a _stack overflow_ if the base case is not sufficient.
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The other fundamental aspect of a recursive function is the recursive step.
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This portion of the function is the step that moves us closer to the base case.
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In an iterative function, this is handled by a loop construct that decrements or increments the counting variable which moves the counter closer to a boolean condition, terminating the loop.
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In a recursive function, the "counting variable" equivalent is the argument to the recursive call.
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If we’re counting down to 0, for example, our base case would be the function call that receives 0 as an argument.
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We might design a recursive step that takes the argument passed in, decrements it by one, and calls the function again with the decremented argument.
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In this way, we would be moving towards 0 as our base case.
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Analyzing the Big O runtime of a recursive function is very similar to analyzing an iterative function. Substitute iterations of a loop with recursive calls.
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Also learn about _Call Stacks and Execution Frames_, it will help understand recursion even better.

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