How to calculate a root node in a Merkle Patricia tree?

Question

I'm trying to understand a Merkle Patricia tree.
For example there are two accounts:
x00: {balance: 1}
x01: {balance: 2}

I can't understand how to begin building my trie. RLP and HP encoding are known, but what is the root node?

Answer 1

Let's take a pseudo-code example:

x00: {balance: 1}
x01: {balance: 2}
x02: {balance: 3}
x03: {balance: 4}

You calculate the first-level nodes:

hashOf("x00: {balance: 1}", "x01: {balance: 2}") -> node1 0x1234 
hashOf("x02: {balance: 3}", "x04: {balance: 3}") -> node2 0x5476

You then calculate the second-level node(s):

hashOf("node1 0x1234", "node2 0x5476") -> node3 0x3981

node3, with the value of 0x3981, is your root node.