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Reverse Polish Notation

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 10

Write a C program to evaluate the value of an arithmetic expression in Reverse Polish Notation (RPN). Valid operators are +, -, *, and /. Each operand may be an integer or another expression. Note that division between two integers should truncate toward zero.

Example 1
    
      
  • Input: tokens = ["2", "1", "+", "3", "*"]
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  • Output: 9
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  • Explanation: Process "2", "1", "+" → 2 + 1 = 3, then "3", "3", "*" → 3 * 3 = 9
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Example 2
    
      
  • Input: tokens = ["4", "13", "5", "/", "+"]
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  • Output: 6
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  • Explanation: Process "13", "5", "/" → 13 / 5 = 2 (truncated), then "4", "2", "+" → 4 + 2 = 6
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Constraints
    
      
  • 1 ≤ tokens.length ≤ 10^4
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  • tokens[i] is either an operator: "+", "-", "*", or "/", or an integer in the range [-200, 200]
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  • The given RPN expression is always valid
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  • The answer and all the intermediate calculations can be represented in a 32-bit integer
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  • Time Complexity: O(n)
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  • Space Complexity: O(n)
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Hint
Solution

Solution Hints

    
      
  • Use a stack data structure to store operands
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  • Iterate through each token in the expression
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  • If the token is a number, push it onto the stack
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  • If the token is an operator, pop two operands from the stack
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  • Apply the operator to the two operands and push the result back onto the stack
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  • The final result will be the only element left in the stack
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Steps to solve by this approach:

 Step 1: Initialize an empty stack to store operands
 Step 2: Iterate through each token in the RPN expression
 Step 3: If the token is a number, convert it to integer and push onto stack
 Step 4: If the token is an operator, pop two operands from the stack
 Step 5: Apply the operator to the two operands (first popped is second operand)
 Step 6: Push the result of the operation back onto the stack
 Step 7: Return the final result which is the only element left in the stack

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