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Basic Calculator

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 15

Write a C program to implement a basic calculator that evaluates a string expression containing non-negative integers, '+', '-', '(' and ')' operators. The expression is guaranteed to be valid and there are no leading zeros in the numbers. Spaces in the expression should be ignored.

Example 1
    
      
  • Input: s = "1 + 1"
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  • Output: 2
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  • Explanation: 
    • Parse the expression "1 + 1". 
    • Perform addition: 1 + 1 = 2. 
    • Therefore, the result is 2.
    •
Example 2
    
      
  • Input: s = " 2-1 + 2 "
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  • Output: 3
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  • Explanation: 
    • Parse the expression "2-1 + 2" (ignoring spaces). 
    • Perform operations left to right: 2 - 1 = 1, then 1 + 2 = 3. 
    • Therefore, the result is 3.
    •
Constraints
    
      
  • 1 ≤ s.length ≤ 3 * 10^5
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  • s consists of digits, '+', '-', '(', ')', and ' '
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  • s represents a valid expression
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  • '+' is not used as a unary operation
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  • '-' could be used as a unary operation but only at the beginning or after '('
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  • Time Complexity: O(n)
    • 
      
  • Space Complexity: O(n)
    •
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Hint
Solution

Solution Hints

    
      
  • Use a stack to handle parentheses and maintain intermediate results
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  • Keep track of the current number being parsed and the operation to perform
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  • When encountering '+' or '-', apply the previous operation and update the operator
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  • When encountering '(', push current result and operator to stack
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  • When encountering ')', pop from stack and combine with current result
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  • Handle spaces by simply ignoring them during parsing
    •

Steps to solve by this approach:

 Step 1: Initialize a stack, result variable, current number, and sign tracker
 Step 2: Iterate through each character in the input string
 Step 3: If digit, build the current number by multiplying by 10 and adding digit
 Step 4: If '+' or '-', add signed number to result, reset number, update sign
 Step 5: If '(', push current result and sign to stack, reset for sub-expression
 Step 6: If ')', complete current sub-expression, pop and combine with previous result
 Step 7: After parsing, add the final number to result and return

Submitted Code :