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How come there are 32 5s being printed ?

Swapnil Mishra

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Campbell Ritchie

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Please format your code correctly: single empty lines between successive methods.
Please use a pencil and paper to follow the order of execution. You will find the loop makes a recursive call repeatedly, and I shall leave it to you to count how many method calls that entails, and also work out why the value of a is when it is printed is 5.

Swapnil Mishra

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Campbell Ritchie wrote:Please format your code correctly: single empty lines between successive methods.
Please use a pencil and paper to follow the order of execution. You will find the loop makes a recursive call repeatedly, and I shall leave it to you to count how many method calls that entails, and also work out why the value of a is when it is printed is 5.

ok

after step 4 step 2 and 3 are repeated back and forth until the condition turns false and breaks out of while loop and from here I am assuming after breaking out of the while loop it should print the last value of a i.e 5 and exit the program

image_2024-02-23_153551374.png

Swapnil Mishra

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can someone please help

Piet Souris

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I put some println's in your code, so that you can see what's going on:

There are three kinds of actuaries: those who can count, and those who can't.

Swapnil Mishra

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Thank you, this should help, I will take some time to understand this.

Swapnil Mishra

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I am not able to understand, someone please explain with respect to the original code.

Campbell Ritchie

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Doing well It isn't difficult to work out how you get 5, is it?

When you call meth17(0), the loop runs 5×
When you call meth17(1), the loop runs 4×
When you call meth17(2), the loop runs thrice
When you call meth17(3), the loop runs twice
When you call meth17(4), the loop runs once

Each pass through the loop creates a recursive call. Those recursive calls call
meth17(++a). Take a larger sheet of paper, or write smaller, and draw a tree with all those calls on. I hope they will add up to 32 calls.
Note this is an inefficient way of running recursion, rather like the following notorious Fibonacci number program:-That program is expensive in terms of execution speed; it runs in O(1.618...ⁿ) time complexity.

Carey Brown

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Here's a less verbose version:
Output:
(Note: '>>' is entering and '<<' is leaving)

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Carey Brown

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Or...
Output:
(Note: '++' is inside loop increment)

0 >>
1 ++
|   1 >>
|   2 ++
|   |   2 >>
|   |   3 ++
|   |   |   3 >>
|   |   |   4 ++
|   |   |   |   4 >>
|   |   |   |   5 ++
|   |   |   |   |   5 >>
|   |   |   |   |   5 <<
|   |   |   |   5 <<
|   |   |   5 ++
|   |   |   |   5 >>
|   |   |   |   5 <<
|   |   |   5 <<
|   |   4 ++
|   |   |   4 >>
|   |   |   5 ++
|   |   |   |   5 >>
|   |   |   |   5 <<
|   |   |   5 <<
|   |   5 ++
|   |   |   5 >>
|   |   |   5 <<
|   |   5 <<
|   3 ++
|   |   3 >>
|   |   4 ++
|   |   |   4 >>
|   |   |   5 ++
|   |   |   |   5 >>
|   |   |   |   5 <<
|   |   |   5 <<
|   |   5 ++
|   |   |   5 >>
|   |   |   5 <<
|   |   5 <<
|   4 ++
|   |   4 >>
|   |   5 ++
|   |   |   5 >>
|   |   |   5 <<
|   |   5 <<
|   5 ++
|   |   5 >>
|   |   5 <<
|   5 <<
2 ++
|   2 >>
|   3 ++
|   |   3 >>
|   |   4 ++
|   |   |   4 >>
|   |   |   5 ++
|   |   |   |   5 >>
|   |   |   |   5 <<
|   |   |   5 <<
|   |   5 ++
|   |   |   5 >>
|   |   |   5 <<
|   |   5 <<
|   4 ++
|   |   4 >>
|   |   5 ++
|   |   |   5 >>
|   |   |   5 <<
|   |   5 <<
|   5 ++
|   |   5 >>
|   |   5 <<
|   5 <<
3 ++
|   3 >>
|   4 ++
|   |   4 >>
|   |   5 ++
|   |   |   5 >>
|   |   |   5 <<
|   |   5 <<
|   5 ++
|   |   5 >>
|   |   5 <<
|   5 <<
4 ++
|   4 >>
|   5 ++
|   |   5 >>
|   |   5 <<
|   5 <<
5 ++
|   5 >>
|   5 <<
5 <<

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Liutauras Vilda

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@Swapnil Mishra

Just want to say one thing, don't feel bad if you don't get it (now or even later). That's certainly not an easy thing to get!
Recursion on its own is mind bending, and then on top of that it is added a confusing code construct.

However, if I'd need to track myself what's going on (I certainly need ), I'd use this code:

Now, run this code, try to visualise in your head and code... I know, easier said than done, no worries if that takes a lot of time - expected.

Campbell Ritchie

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Liutauras Vilda wrote:. . . Recursion on its own is mind bending . . .

I gave up trying to understand it ages ago. It works, and that is that. (See Happiness by A A Milne.

Campbell Ritchie

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Did you get 32 occurrences of the System.out.println() call, Carey?

Campbell Ritchie

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A few hours ago, I wrote:Did you get 32 occurrences . . .

I tried adding a count variable to your class and that did come to 32.

Chris Smithtopher

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I'm going to take some time to study this myself.

On a different note, I think we've found a great way to generate some ski slopes, courtesy of Carey

Swapnil Mishra

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After racking my brain for 1.5 days straight I finally understood the code on my own, and understood how recursions work inside the loop, feels soo satisfying when you kill a confusion. But thanks a ton, to each and everyone, it really really helped me a lot.

Sometimes staying in confusion really irritates you and pushes you to brings the best out of you, although I understand that using recursion inside the loop is not very practical, is something which you do not see very often, but sometimes my monkey mind poses such weird questions, which I like to solve and understand because It makes you understand how code really works and It also teaches you a lot and reveals many new information at microscopic level.

𝘐𝘯 𝘵𝘩𝘦 𝘤𝘢𝘷𝘦 𝘰𝘧 𝘊𝘰𝘯𝘧𝘶𝘴𝘪𝘰𝘯, 𝘊𝘶𝘳𝘪𝘰𝘴𝘪𝘵𝘺 𝘪𝘴 𝘵𝘩𝘦 𝘰𝘯𝘭𝘺 𝘳𝘢𝘺 𝘰𝘧 𝘩𝘰𝘱𝘦.

Tried with smaller value of 'a' to reduce iterations and confusion (since 2 will be closer to base case condition)
also the initial call stack is colored to ease understanding

when a=2

meth17(3)→meth17(4)→meth17(5) prints 5 then unwind from stack meth17(5) prints 5

meth17(4)meth17(5) prints 5 then unwind from stack meth17(5) prints 5

meth17(3)meth17(4)meth17(5) prints 5 again unwinding from call stack meth17(5) prints 5 again meth17(4)meth17(5) prints 5 meth17(3)meth17(4)meth17(5) prints 5

This is my explanation, (skips condition checks)
It might not be as friendly to understand as compared to some of the explanations posted here, but please bear with me.

P.S : I recommend folks to avoid using pen and paper to dry run manually, and try the Eclipse Debugger instead with breakpoints at desired lines, while keeping the visual perspective setting on, it really helped a lot.

Carey Brown

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Swapnil Mishra wrote:I understand that using recursion inside the loop is not very practical, is something which you do not see very often

Actually, recursion inside a loop happens quite often.

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Swapnil Mishra

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Carey Brown wrote:

Swapnil Mishra wrote:I understand that using recursion inside the loop is not very practical, is something which you do not see very often

Actually, recursion inside a loop happens quite often.

Keeping the philosophical quotes aside, please don't tell me software developers in the industry actually come across these situations (recursion inside a loop).
because a day ago It was looking like a nightmare to me and impossible to comprehend. 😅😅😅

Chris Smithtopher

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Swapnil Mishra wrote:

Carey Brown wrote:

Swapnil Mishra wrote:I understand that using recursion inside the loop is not very practical, is something which you do not see very often

Actually, recursion inside a loop happens quite often.

Keeping the philosophical quotes aside, please don't tell me software developers in the industry actually come across these situations (recursion inside a loop).
because a day ago It was looking like a nightmare to me and impossible to comprehend. 😅😅😅

Knowing life and people, I'm sure they encounter far worse, even if it's not intentional.

Swapnil Mishra

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Chris Smithtopher wrote:Knowing life and people, I'm sure they encounter far worse, even if it's not intentional.

😟😯

Carey Brown

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Swapnil Mishra wrote:please don't tell me software developers in the industry actually come across these situations (recursion inside a loop).
because a day ago It was looking like a nightmare to me and impossible to comprehend. 😅😅😅

Traversing a "tree" happens quite frequently. Think about visiting all files in a directory tree.

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Campbell Ritchie

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Yesterday, I wrote:. . . I gave up trying to understand [recursion] ages ago. . . .

Swapnil Mishra

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when a=0

meth1meth2meth3meth4meth5 false prints 5
└───────meth5 false prints 5
└───────meth4meth5 false prints 5
└────────meth5 false prints 5
└───────meth3meth4meth5 false prints 5
└────────meth5 false prints 5
└────────meth4meth5 false prints 5
└────────meth5 false prints 5
└───────meth2meth3meth4meth5 false prints 5
└────────meth5 false prints 5
└────────meth4meth5 false prints 5
└────────meth5 false prints 5
└────────meth3meth4meth5 false prints 5
└────────meth5 false prints 5
└────────meth4meth5 false prints 5
└─────────meth5 flase prints 5
└───────meth1meth2meth3meth4meth5 false prints 5
└────────meth5 false prints 5
└────────meth4meth5 false prints 5
└────────meth5 false prints 5
└────────meth3meth4meth5 false prints 5
└────────meth5 false prints 5
└────────meth4meth5 false prints 5
└─────────meth5 false prints 5
└────────meth2meth3meth4meth5 false prints 5
└────────meth5 false prints 5
└────────meth4meth5 false prints 5
└─────────meth5 false prints 5
└────────meth3meth4meth5 false prints 5
└─────────meth5 false prints 5
└─────────meth4meth5 false prints 5
└────────meth5 false prints 5

Liutauras Vilda

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Swapnil Mishra

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Liutauras Vilda wrote:?

Hint : Try Tree Command in CMD and you might get the Hierarchical Structure of Directories (Directory Tree) You might get what I am trying to say

Also I'm quiet bad at explaining I used lots of shortcuts instead of writing prints 5 just wrote prints for meth17() wrote meth() sorry for that 😅
method 5 stacks upon method 4 , method 4 stacks upon method 3 upon method on 2 and finally on 1 and then unwinding starts from backwards (stacks executes in LIFO order)

Liutauras Vilda

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Cowgratulations, Swapnil! Your topic has been published in our CodeRanch's February 2024 Edition Journal

hans brink

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For investigation a nice try, but will ever in history a recursion inside
a while loop be needed as solution for a programming task?
Maybe in a rare case a loop inside a recursion.
I looked on internet in the search engine and see mostly
recursion OR a loop.
recursion for a recursive structure and a loop for a loop structure.
So i think be not worried about need of much study time.
It is maybe an insane mixture..?

Mike Simmons

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No, recursion inside a loop is a normal thing. See Carey's "Traversing a "tree" happens quite frequently" post above.

Swapnil Mishra

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Liutauras Vilda wrote:Cowgratulations, Swapnil! Your topic has been published in our CodeRanch's February 2024 Edition Journal

😮😀😃 Woa! Awesome!