Similarity Between SLR(1), LALR(1), and LR(1): Correct Choice and Learning Path

When comparing SLR(1), LALR(1), and LR(1), all three are bottom-up LR-family parsing methods that construct an LR automaton of items and produce an LR parsing table. The key distinction is how lookahead information is computed and used when building the parsing table.

In particular:

• LR(1) is based on the full set of canonical LR(1) items (items include lookahead sets).
• LALR(1) starts from LR(1) structure but merges states that have the same LR(0) core, combining/propagating lookahead sets to form an LALR(1) parsing table.
• SLR(1) uses only FOLLOW sets of nonterminals as lookaheads, producing a more approximate (but simpler) parsing table.

A direct implication for your multiple-choice options is that their parsing tables are not the same, nor are their underlying item/lookahead construction algorithms identical—though they share the same general LR(1)-style bottom-up machinery.

Therefore, the correct choice is: (iv) Both parsing tables and algorithms are different.

Key learning terms

• LR(1) items
• LR(0) core
• FOLLOW set
• LALR(1) merging

How the LR-family differs (conceptual mapping to the options)

A useful way to align theory to the given options:

1. Not (i): “Use of same algorithm, but different parsing table.”
   SLR/LALR/LR differ in how lookaheads are generated for items/table entries (FOLLOW-based vs canonical lookaheads vs merged lookahead propagation). That is algorithmic, not just table differences.

2. Not (ii): “Same parsing table, but different algorithm.”
   If the parsing table were the same, then lookahead computation would effectively be the same as far as correctness conflicts go—this is not the case across the three methods.

3. Not (iii): “Tables and algorithms similar but use top-down approach.”
   These are bottom-up LR methods, not top-down (top-down methods are typically LL(1), recursive descent with predictive parsing, etc.).

4. Yes (iv): “Both parsing tables and algorithms are different.”

   • LR(1): canonical lookaheads per item (largest, most precise)
   • LALR(1): merges states with same LR(0) core (less precise than LR(1), more than SLR(1))
   • SLR(1): approximates lookahead using FOLLOW sets (simplest, potentially more conflicts)