If you remove the LCR and PoW, all you are left with is a toy example which cannot work in practice.
What is needed is education about censensus design and bitcoin's implementation of the solution, rather than a 'how to guide' for building a basic linked list under the guise of 'blockchain'.
Cheers, Paul.
Add a field to store a random number. Keep generating values for this field until the hash of the structure has 'n' leading zeros.
Is that more or less correct?
This sounds pretty interesting, can you elaborate on how exactly its proxy model for the passage of time?
You need an analogue to elapsed time to solve this problem. Hashes in bitcoin are probabilistic, there is an expected number of hashes required to solve the PoW (on average). Each hash takes an amount of time that cannot be made faster, so you suddenly have an unforgeable, easily provable analogue to elapsed time.
It's worth adding to that description that the hash must be secure in that it does not allow determining what random number to use to get a particular output (I'm sure you already recognized this detail - it just guarantees you have to keep trying actually random numbers to find a result).
Also worth adding is that the 'n' (Basically the difficulty) is generally going to need some way of scaling based on how quickly correct hashes were found in the past. This is important to prevent problems that would happen with people being able to generate correct results too quickly (Or even just significantly faster then previously).
In particular, Bitcoin's difficulty factor scales such that a new block is found aprox. every 10 minutes, so 'n' is adjusted every so many blocks depending on how fast the hashes were found. Because in the case of Bitcoin, a found block means more coins in the market, it is important that when more hashing power is added, it doesn't result in blocks now being found 1 minute apart. If that were to happen, then you'd have 10 times the number of coins entering the market.
[ed: from other comments, I gather that "passage of time" means "added blocks (hashes)" - but I'm still not clear on where the agreement on what constitutes "in 10 minutes on average" comes from - if A sees an addition to the blockchain of N blocks with X proof-of-work, lets call it N * X from B, and sees M blocks with Y proof-of-work from C -- it should be easy to figure out which is bigger of N * X and M * Y (here we don't really assume multiplication, but some way to figure out maximum proof-of-work).
But how does A know how long either took? Is the time local, so that A looks at the head of the B and C chains, and considers when A saw this head, and figure the elapsed time based on that?]
It's also worth keeping in mind the problem that timestamps are technically forge-able by the miner. Bitcoin doesn't really solve this problem, but it does place requirements that the timestamp of a block be larger then the average of the past 11 (With various constraints). Thus if you presumably have mining distributed enough, then one giving you as invalid of a time as would still be accepted wouldn't end-up affecting things long-term since they can't generate blocks fast enough to heavily affect the average. Still technically an attack vector though.
In that situation, A doesn't care how long it actually took to find those blocks, the scaling of the difficulty/work-factor handles that. A can rely on the fact that (Unless someone introduced or removed a significant chunk of hashing power, or broke the hashing algorithm) the current network difficulty represents the amount of work needed to represent approximately '10 minutes'. PoW below that difficulty isn't accepted, and above that would be considered proving more work then required (But is also, of course, harder to find. So it proves more, but should take longer then 10 minutes for the network to find).
Since Bitcoin calculates the difficulty to result in about 10 minutes between blocks (As I explained in my last comment), that's how long it should approximately take. It's possible B or C got lucky and found it faster then that, but statistically that is unlikely since the hash result is completely random. If significantly more hashing power is added to the network and the blocks are consistently found faster then the target time, then when the difficulty is recalculated later-on (After the 2016 blocks are done) it will go-up, making them again take about 10 minutes with the hew hashing power taken into account.
Now to actually answer your question: if you take 2 bitcoin blockchains that stem from the same origin block, but blockchainA has 20 blocks with a very easy target "fffffffdab3" and blockchainB has 1 block with a very difficult target "00000000003", then blockchainB has actually done more work than blockchainA, even though it has less blocks (it is "shorter"). So blockchainB has the most cumulative proof of work.