What is the difference between a leftmost derivation and a rightmost derivation?

What is the difference between a leftmost derivation and a rightmost derivation?

The main difference between a leftmost derivation and a rightmost derivation lies in the order in which the non-terminal symbols are replaced by their corresponding production rules.

In a leftmost derivation, the leftmost non-terminal symbol in a string is always replaced first. This means that at each step, the leftmost non-terminal symbol is expanded using its production rule. This process continues until all non-terminal symbols are replaced by terminal symbols, resulting in a leftmost derivation.

On the other hand, in a rightmost derivation, the rightmost non-terminal symbol in a string is always replaced first. This means that at each step, the rightmost non-terminal symbol is expanded using its production rule. This process continues until all non-terminal symbols are replaced by terminal symbols, resulting in a rightmost derivation.

In summary, the difference between a leftmost derivation and a rightmost derivation is the order in which the non-terminal symbols are expanded.