ITPEC FE Morning October 2019 Question 5

Postfix Expression Evaluation — evaluate a reverse Polish notation expression using a stack.

Expression: 5 4 6 + × 4 9 3 ÷ + ×

Step-by-step stack trace:

• •5 → stack: [5]
• •4 → stack: [5, 4]
• •6 → stack: [5, 4, 6]
• •+ → 4 + 6 = 10 → stack: [5, 10]
• •× → 5 × 10 = 50 → stack: [50]
• •4 → stack: [50, 4]
• •9 → stack: [50, 4, 9]
• •3 → stack: [50, 4, 9, 3]
• •÷ → 9 ÷ 3 = 3 → stack: [50, 4, 3]
• •+ → 4 + 3 = 7 → stack: [50, 7]
• •× → 50 × 7 = 350 → stack: [350]

Result: 350

Why not others:
- (a) 98 — incorrect arithmetic sequence
- (b) 154 — incorrect arithmetic sequence
- (c) 238 — incorrect arithmetic sequence

Key rule: In postfix evaluation, scan left to right. Push operands onto a stack. When an operator appears, pop two operands (second popped is the left operand), apply the operator, and push the result back.

AI-generated — may contain errors