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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). RPN is a mathematical notation in which every operator follows all of its operands, for example: ["2", "1", "+", "3", "*"] represents (2 + 1) * 3 = 9. The valid operators are '+', '-', '*', and '/'. Each operand may be an integer or another expression. Division between two integers always truncates toward zero.

Example 1
    
  
  • Input: tokens = ["2", "1", "+", "3", "*"]
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  • Output: 9
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  • Explanation: 
    
      
      
    • ((2 + 1) * 3) = 9
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Example 2
    
  
  • Input: tokens = ["4", "13", "5", "/", "+"]
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  • Output: 6
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  • Explanation: 
    
      
      
    • (4 + (13 / 5)) = 4 + 2 = 6
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    • (Note that 13 / 5 = 2.6, but integer division truncates to 2.)
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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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  • Time Complexity: O(n)
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  • Space Complexity: O(n)
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StackD. E. ShawArctwist
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Hint
Solution

Solution Hints

    
  
  • Use a stack to keep track of operands
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  • When an operator is encountered, pop the required number of operands from the stack
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  • Evaluate the expression with the operator and push the result back onto the stack
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  • At the end, the stack will contain the final result
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  • Be careful with division, as it truncates toward zero
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Steps to solve by this approach:

 Step 1: Create a stack to store operands.

 Step 2: Iterate through each token in the input array.

 Step 3: If the token is a number, push it onto the stack.

 Step 4: If the token is an operator, pop the top two operands from the stack.

 Step 5: Evaluate the expression with the operator and the two operands.

 Step 6: Push the result of the evaluation back onto the stack.

 Step 7: After processing all tokens, the only item left on the stack is the final result.

Submitted Code :