DFA | Deterministic Finite Automata | Common Symbols Examples Part 2

This is Part 2 of our DFA Examples Series, where we continue solving important exam-style problems on common symbol constraints. These examples build on Part 1 and take you deeper into DFA design by covering counting, multiple conditions, and advanced symbol-based requirements.

🔍 What You’ll Learn in This Lecture

1. DFA with Counting Occurrences

DFA that accepts strings with at least two occurrences of a symbol

DFA that accepts strings with exactly two occurrences of a symbol

2. DFA with Multiple Conditions

DFA that accepts strings containing both symbols (0 and 1)

DFA that accepts strings containing both a and b

3. DFA with Exclusion & Restriction

DFA that accepts strings with no two consecutive 1s

DFA that accepts strings with no two consecutive a’s

🧑‍💻 Technical Insight (Detailed)

In these problems, the DFA construction requires state tracking for counts and conditions. For example:

Counting Occurrences:

States represent “number of times a symbol has been seen so far.”

For “exactly 2 occurrences,” a dead state is added once more than 2 are encountered.

Multiple Conditions:

States track whether each required symbol has been seen.

Accepting states are defined only when both conditions are satisfied.

Consecutive Symbol Restrictions:

States represent “last symbol read.”

A dead state handles invalid consecutive patterns.

These examples demonstrate how DFA states encode memory of previous input to enforce global string properties.

🖊 Example Problems Covered (Part 2)

DFA over {0,1} that accepts strings with at least two 1s

DFA over {a,b} that accepts strings with exactly two as

DFA over {0,1} that accepts strings containing both 0 and 1

DFA over {a,b} that accepts strings containing both a and b

DFA over {0,1} that accepts strings with no two consecutive 1s

🕒 Timestamps

0:00 – Introduction & recap of Part 1
2:40 – Example 1: At least two occurrences
7:15 – Example 2: Exactly two occurrences
12:30 – Example 3: Contains both symbols
17:00 – Example 4: Contains both a and b
22:10 – Example 5: No two consecutive symbols
28:30 – Summary & practice tips

📂 Resources:

📥 Download DFA practice problems (with solutions) → [Your link]
📺 Next lecture: Common Symbols Examples Part 3 → [Your link]

🔍 Keywords:

DFA common examples part 2

DFA examples counting symbols

DFA exactly two occurrences

DFA at least two occurrences

DFA contains both symbols

DFA no consecutive symbols

DFA examples with restrictions

DFA multiple condition examples

DFA solved problems part 2

DFA state diagram exam questions

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