ORIGINAL CODING QUESTION
Evaluate postfix instructions
Evaluate a valid postfix expression. Operands are integers -10..10; tokens 101,102,103 mean addition, subtraction and multiplication. Subtraction uses left operand minus right operand.
Original exercise · medium. Editorial role relevance does not imply a company has asked this question.
Input and output
n, followed by n postfix tokens. Print the final integer.
Constraints
1 ≤ n ≤ 15; expression is valid; intermediate/final results fit signed 32-bit integers.
Example 1
Input
5 2 3 101 4 103
Output
20
(2+3)*4 is 20.
Example 2
Input
3 2 5 102
Output
-3
2-5 is -3.
Explain your approach
Explain your time and auxiliary space complexity. Which input makes your algorithm work hardest?
Private grading inputs, expected outputs and canonical reference implementations are withheld. Authored expected outputs were cross-checked with independent reference oracles; compiler/runtime behavior still needs a verified execution provider.
Hint 1
Operands wait on a stack until an operator arrives.
Hint 2
Pop the right operand before the left operand.
Hint 3
Evaluate left op right and push the result.
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