A lot of my personal opinion follows, and I'd be very, very happy to hear dissenting opinions! I believe there are at least two valid goals for learning that are relevant to memorization:
1) Learning for mastery / competency to apply the skills to real life endeavors
2) Learning so you can meet some standard necessary to enable certain opportunities in life
It seems your opinion comes from a personal value bias towards #2 and I share that bias, but perhaps not as dominantly as you do (at the moment). For both of these, memorization can be very helpful, even optimal. But the application of spaced repetition would be different depending on the goal.
On memorization applied to learning for genuine personal mastery:
I believe memorization is optimal for foundational axiomatic knowledge. A good example is quick addition and times tables (and other arithmetic). I believe:
1) People should consider it a necessary life skill to be able to perform reasonably complex arithmetic manually in your head. For example, 4462+9241=13703 or 25120=3000. Many people will disagree on the nuances on where this begins and ends, and that's okay. For example some people will feel that people should be able to multiple 27123 in their head, others would feel it's okay for something like that to be done on paper. But for me, the point is that there exists a category like "things you should be able to do, but it's fine not to have memorized". More importantly, I believe it would be suboptimal to spend a significant amount of your life memorizing an increasing sample of these, but it's reasonable to spend time maintaining the skill of manual mental arithmetic and probably reasonable to spend time improving the speed and accuracy with which you do it.
-- 1a) A nuanced subset of this skill example is "estimation", for situations where it's appropriate. It might take longer for some people to manually calculate 27123 (or whatever) than for them to pull out their cell phone or ask their Apple Watch. If the situation only needs them to have an upper and lower bound within they might break it down to {lower_bound = 25120 = ((256)2)10 = (150210) = 3000; upper_bound = 30125 = 3055 = 150510/2 = 75010/2 = 7500/2 = 3750} and they could determine the answer is around 3350 or so, but absolutely 100% definitely between 3000 and 3750. And they could still do this type (if not degree) of estimation faster (and more stealthily, which can be important sometimes, like during negotiations/haggling) than pulling out a cellphone and calculating.
2) People absolutely cannot do arithmetic if they do not have certain foundational axioms memorized. If you do not have 1+1=2, 2+1=3, 3+1=4, etc memorized (counting), you literally cannot do arithmetic. That would be an absurdly low-functioning adult and essentially means you don't know how to count. But technically* you only need to be able to count to add, subtract, and multiply (by maintaining two counts simultaneously) any real numbers. Obviously just counting is a helpful, but not optimal, level of memorized knowledge to be competent at arithmetic. It would plainly be helpful to also memorize things like 7+6=13 and 152 = 30, and have instant recall for these rather than re-calculating them manually every time you need them. Which brings me to:
-- 2a) I believe it is helpful to memorize more than what many people think it is helpful to memorize. We generally are taught in primary school to memorize times tables up to 10x10. But perhaps it would be useful to extend this beyond 10x10, at minimum for some additional prime numbers which might show up frequently and cannot be quickly factored to smaller numbers. I could see it being super nice to have my times tables memorized up to 100x100, and additional addition/substraction memorized. I feel this way because despite having done well in three semesters of calculus and differential equations, I have always had a few "holes" in my brain's lookup table for certain simple addition and multiplication - specifically it really slows me down to need to manually calculate 86 (I have to do 832) or add 16+7 (I personally have to do 20+4+3). It's very frustrating to hit these basic roadblocks. Often I wonder how much happier I'd be if, at a young age, I had personally chosen to endeavor to memorize an unusually large amount of basic integer combinations, rather than just focus on memorizing the minimum necessary to get 100% on my K-5 coursework. Why do I not know 86? Because I took the less ambitious route of just breaking it down to 446 or 823 every time. Which brings me to:
On memorization for learning so that you can meet some standard necessary to enable certain opportunities in life:
1) I think we can all agree that some things are worth striving for, but are gated behind formal or informal tests which aren't relevant to the skills and temperament that actually enable people who do those things to do them well. For many people, that's "leetcode", but it can also be things like a college graduate memorizing and practicing ad nauseam a powerpoint delivery for a technical role for which they'll never formally present anything in their entire career. It could also be memorizing certain key motifs in a history or politics or English class which are actually wrong. The student may even know* its wrong, but it must still be memorized and regurgitated to get the best possible grade for their transcript.
1a) I think we can all agree that when cramming for an exam for which knowledge is not particularly desired to be retained, the best memorization technique is the one that takes the least amount of time to remember the facts just long enough to regurgitate them for the exam. I've discovered that this method is not the most commonly evangelized "spaced" repetition, but rather a Leitner system implemented in a way such that you actually minimize the time spacing as much as possible. For me, this uses digital or physical flash cards. Make a deck containing all facts you want to be able to maccess n days later during the exam. Go through the deck one at a time and any you get correctly, move to a new pile on the right; any you get wrong, move to a new pile on the left. Keep going repeating this with the left-most pile without breaks or pauses until you are getting enough % correct to get the desired score on the exam (with some safety margin), or you get exhausted or stop improving (then sleep and do it again the next day). This takes up far less actual time than spaced repetition, but you'll also forget the information fairly quickly as well and retain much less of it permanently.
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To bring it back to the actual topic of memorizing leetcode: For me personally, I think memorizing some leetcode can be useful in three ways.
1) (For both mastery and credentialism) This is stretching the definition of leetcode a lot, but it's worth mentioning. I think it's a good idea to memorize syntax and functions/methods of the language, libraries, frameworks, and tools that you intend to use. I switch languages a lot at work, and I switch jobs a lot. It genuinely shocks me how much I can accomplish in some languages for which I can't even write a syntactically correct for-loop. Like if you put a blank paper and a pen in front of me, I could not write a for-loop -- but I can copy/paste one loop from language documentation or google result or ChatGPT and then copy/paste that line from my source code over and over until I have a working API or application or website from scratch in under a day. But I hate it, and not knowing all the syntax makes me slower. Not knowing what methods are available for a certain class is very frustrating. I don't need to have it memorized to do my job, but when I'm working in a language that I do know super-well, I have a much happier time doing the job.
2) (For mastery) Some leetcode could be considered "merely slightly more complex fundamental concepts". Nobody would argue that you should be able to write a for loop from memory in your language, but I think it's reasonable to say that it could very well be useful to be able to have instant recall of some amount of slightly more complex algorithms rather than needing to google them, like implementing sliding windows using trees. Or (for low-resource embedded programming) things like exponentially weighted moving average. Etc. What these are depends on what you desire to have mastery over, but memorization via spaced repetition can ensure that these "leetcode" techniques are always available to you the instant you need to implement them.
3) (For credentialism) Yes, it would be wonderful if we all had the brainpower to instantly figure out all leetcode problems fluently on the fly without awkward pauses. But most programmers can't, and it's better for the interviews if you can quickly, decisively, and confidently present everything that the interviewers are looking for. For this, I believe it can be genuinely worth spending some of your life memorizing leetcode if it means the difference between making $120,000 vs. $225,000 for the next five years. You probably won't ever use two-sum or flood-fill in your real job, but if it's the requirement to get that job, it can make a massive difference in your quality of life. Offloading brain-processing by memorizing leetcode also allows you to spend more of your higher-level thinking on connecting with your interviewers, figuring out the best presentation style tailored to them, and optimizing emotional expression during the leetcode portions of the interviews. Basically, leetcode isn't the only "hard" part of interviews, and it's useful to free up as much brainpower as possible available for the other challenging things that you need to handle simultaneously as well. Most of those other things don't have a "ceiling", any additional marginal efficacy might make the difference. I believe spaced repetition is best here instead of time-minimized Leitner method, because not only is it helpful to still have much of this memorized two years later when you might desire to interview again, but also because the complexity of the problems makes a time-minimized approach fairly infeasible.
On the topic of memorising arithmetic, I have found it surprisingly useful to memorise a few base ten logarithms. While most people have a good sense of numbers as an arithmetic progression, the geometric perspective is often more useful. (Things like how 3 is halfway from 1 to 10, but 10 is halfway from 1 to 100. (This is just the square root, of course, since that is a power of a half. But it's also useful to know that 2 is one-third of the way to 10, and 1.6 is a tenth of the way to 100. I.e. knowing some logarithms, you can mentally compute arbitrary fractional powers in your head.))
1) Learning for mastery / competency to apply the skills to real life endeavors
2) Learning so you can meet some standard necessary to enable certain opportunities in life
It seems your opinion comes from a personal value bias towards #2 and I share that bias, but perhaps not as dominantly as you do (at the moment). For both of these, memorization can be very helpful, even optimal. But the application of spaced repetition would be different depending on the goal.
On memorization applied to learning for genuine personal mastery:
I believe memorization is optimal for foundational axiomatic knowledge. A good example is quick addition and times tables (and other arithmetic). I believe:
1) People should consider it a necessary life skill to be able to perform reasonably complex arithmetic manually in your head. For example, 4462+9241=13703 or 25120=3000. Many people will disagree on the nuances on where this begins and ends, and that's okay. For example some people will feel that people should be able to multiple 27123 in their head, others would feel it's okay for something like that to be done on paper. But for me, the point is that there exists a category like "things you should be able to do, but it's fine not to have memorized". More importantly, I believe it would be suboptimal to spend a significant amount of your life memorizing an increasing sample of these, but it's reasonable to spend time maintaining the skill of manual mental arithmetic and probably reasonable to spend time improving the speed and accuracy with which you do it.
-- 1a) A nuanced subset of this skill example is "estimation", for situations where it's appropriate. It might take longer for some people to manually calculate 27123 (or whatever) than for them to pull out their cell phone or ask their Apple Watch. If the situation only needs them to have an upper and lower bound within they might break it down to {lower_bound = 25120 = ((256)2)10 = (150210) = 3000; upper_bound = 30125 = 3055 = 150510/2 = 75010/2 = 7500/2 = 3750} and they could determine the answer is around 3350 or so, but absolutely 100% definitely between 3000 and 3750. And they could still do this type (if not degree) of estimation faster (and more stealthily, which can be important sometimes, like during negotiations/haggling) than pulling out a cellphone and calculating.
2) People absolutely cannot do arithmetic if they do not have certain foundational axioms memorized. If you do not have 1+1=2, 2+1=3, 3+1=4, etc memorized (counting), you literally cannot do arithmetic. That would be an absurdly low-functioning adult and essentially means you don't know how to count. But technically* you only need to be able to count to add, subtract, and multiply (by maintaining two counts simultaneously) any real numbers. Obviously just counting is a helpful, but not optimal, level of memorized knowledge to be competent at arithmetic. It would plainly be helpful to also memorize things like 7+6=13 and 152 = 30, and have instant recall for these rather than re-calculating them manually every time you need them. Which brings me to:
-- 2a) I believe it is helpful to memorize more than what many people think it is helpful to memorize. We generally are taught in primary school to memorize times tables up to 10x10. But perhaps it would be useful to extend this beyond 10x10, at minimum for some additional prime numbers which might show up frequently and cannot be quickly factored to smaller numbers. I could see it being super nice to have my times tables memorized up to 100x100, and additional addition/substraction memorized. I feel this way because despite having done well in three semesters of calculus and differential equations, I have always had a few "holes" in my brain's lookup table for certain simple addition and multiplication - specifically it really slows me down to need to manually calculate 86 (I have to do 832) or add 16+7 (I personally have to do 20+4+3). It's very frustrating to hit these basic roadblocks. Often I wonder how much happier I'd be if, at a young age, I had personally chosen to endeavor to memorize an unusually large amount of basic integer combinations, rather than just focus on memorizing the minimum necessary to get 100% on my K-5 coursework. Why do I not know 86? Because I took the less ambitious route of just breaking it down to 446 or 823 every time. Which brings me to:
On memorization for learning so that you can meet some standard necessary to enable certain opportunities in life:
1) I think we can all agree that some things are worth striving for, but are gated behind formal or informal tests which aren't relevant to the skills and temperament that actually enable people who do those things to do them well. For many people, that's "leetcode", but it can also be things like a college graduate memorizing and practicing ad nauseam a powerpoint delivery for a technical role for which they'll never formally present anything in their entire career. It could also be memorizing certain key motifs in a history or politics or English class which are actually wrong. The student may even know* its wrong, but it must still be memorized and regurgitated to get the best possible grade for their transcript.
1a) I think we can all agree that when cramming for an exam for which knowledge is not particularly desired to be retained, the best memorization technique is the one that takes the least amount of time to remember the facts just long enough to regurgitate them for the exam. I've discovered that this method is not the most commonly evangelized "spaced" repetition, but rather a Leitner system implemented in a way such that you actually minimize the time spacing as much as possible. For me, this uses digital or physical flash cards. Make a deck containing all facts you want to be able to maccess n days later during the exam. Go through the deck one at a time and any you get correctly, move to a new pile on the right; any you get wrong, move to a new pile on the left. Keep going repeating this with the left-most pile without breaks or pauses until you are getting enough % correct to get the desired score on the exam (with some safety margin), or you get exhausted or stop improving (then sleep and do it again the next day). This takes up far less actual time than spaced repetition, but you'll also forget the information fairly quickly as well and retain much less of it permanently.
--------------
To bring it back to the actual topic of memorizing leetcode: For me personally, I think memorizing some leetcode can be useful in three ways.
1) (For both mastery and credentialism) This is stretching the definition of leetcode a lot, but it's worth mentioning. I think it's a good idea to memorize syntax and functions/methods of the language, libraries, frameworks, and tools that you intend to use. I switch languages a lot at work, and I switch jobs a lot. It genuinely shocks me how much I can accomplish in some languages for which I can't even write a syntactically correct for-loop. Like if you put a blank paper and a pen in front of me, I could not write a for-loop -- but I can copy/paste one loop from language documentation or google result or ChatGPT and then copy/paste that line from my source code over and over until I have a working API or application or website from scratch in under a day. But I hate it, and not knowing all the syntax makes me slower. Not knowing what methods are available for a certain class is very frustrating. I don't need to have it memorized to do my job, but when I'm working in a language that I do know super-well, I have a much happier time doing the job.
2) (For mastery) Some leetcode could be considered "merely slightly more complex fundamental concepts". Nobody would argue that you should be able to write a for loop from memory in your language, but I think it's reasonable to say that it could very well be useful to be able to have instant recall of some amount of slightly more complex algorithms rather than needing to google them, like implementing sliding windows using trees. Or (for low-resource embedded programming) things like exponentially weighted moving average. Etc. What these are depends on what you desire to have mastery over, but memorization via spaced repetition can ensure that these "leetcode" techniques are always available to you the instant you need to implement them.
3) (For credentialism) Yes, it would be wonderful if we all had the brainpower to instantly figure out all leetcode problems fluently on the fly without awkward pauses. But most programmers can't, and it's better for the interviews if you can quickly, decisively, and confidently present everything that the interviewers are looking for. For this, I believe it can be genuinely worth spending some of your life memorizing leetcode if it means the difference between making $120,000 vs. $225,000 for the next five years. You probably won't ever use two-sum or flood-fill in your real job, but if it's the requirement to get that job, it can make a massive difference in your quality of life. Offloading brain-processing by memorizing leetcode also allows you to spend more of your higher-level thinking on connecting with your interviewers, figuring out the best presentation style tailored to them, and optimizing emotional expression during the leetcode portions of the interviews. Basically, leetcode isn't the only "hard" part of interviews, and it's useful to free up as much brainpower as possible available for the other challenging things that you need to handle simultaneously as well. Most of those other things don't have a "ceiling", any additional marginal efficacy might make the difference. I believe spaced repetition is best here instead of time-minimized Leitner method, because not only is it helpful to still have much of this memorized two years later when you might desire to interview again, but also because the complexity of the problems makes a time-minimized approach fairly infeasible.