Validation of Equation Given as String

Given a string in the form of an equation i.e A + B + C – D = E where A, B, C, D and E are integers and -, + and = are operators. The task is to print Valid if the equation is valid else print Invalid.
Note: String only comprises of the characters from the set {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, +, -, =}.

Examples:

Input: str = “1+1+1+1=7”
Output: Invalid



Input: str = “12+13-14+1=12”
Output: Valid

Approach:

  • Traverse the string and store all the operands in an array operands[] and all the operators in an array operators[].
  • Now perform the arithmetic operation stored in operators[0] on operands[0] and operands[1] and store it in ans.
  • Then perform the seconds arithmetic operation i.e. operators[1] on ans and operators[2] and so on.
  • Finally, compare the ans calculated with the last operand i.e. operands[4]. If they’re equal then print Valid else print Invalid.

Below is the implementation of the above approach:

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function that returns true if the equation is valid
bool isValid(string str)
{
    int k = 0;
    string operands[5] = "";
    char operators[4];
    long ans = 0, ans1 = 0, ans2 = 0;
    for (int i = 0; i < str.length(); i++) {
  
        // If it is an integer then add it to another string array
        if (str[i] != '+' && str[i] != '=' && str[i] != '-')
            operands[k] += str[i];
        else {
            operators[k] = str[i];
  
            // Evaluation of 1st operator
            if (k == 1) {
                if (operators[k - 1] == '+')
                    ans += stol(operands[k - 1]) + stol(operands[k]);
  
                if (operators[k - 1] == '-')
                    ans += stol(operands[k - 1]) - stol(operands[k]);
            }
  
            // Evaluation of 2nd operator
            if (k == 2) {
                if (operators[k - 1] == '+')
                    ans1 += ans + stol(operands[k]);
  
                if (operators[k - 1] == '-')
                    ans1 -= ans - stol(operands[k]);
            }
  
            // Evaluation of 3rd operator
            if (k == 3) {
                if (operators[k - 1] == '+')
                    ans2 += ans1 + stol(operands[k]);
  
                if (operators[k - 1] == '-')
                    ans2 -= ans1 - stol(operands[k]);
            }
            k++;
        }
    }
  
    // If the LHS result is equal to the RHS
    if (ans2 == stol(operands[4]))
        return true;
    else
        return false;
}
  
// Driver code
int main()
{
    string str = "2+5+3+1=11";
    if (isValid(str))
        cout << "Valid";
    else
        cout << "Invalid";
  
    return 0;
}

chevron_right






                        filter_none









Python3














                                    filter_none




                                    edit

                                    close




                                    play_arrow




                                    link

                                    brightness_4

                                    code
                                




















# Python3 implementation of the approach  


  


# Function that returns true if  


# the equation is valid  


def isValid(string) : 


      


    k = 0;  


    operands = [""] * 5 ;  


    operators = [""] * 4 ;  


    ans = 0 ; ans1 = 0; ans2 = 0;  


    for i in range(len(string)) :  


  


        # If it is an integer then add  


        # it to another string array  


        if (string[i] != '+' and 


            string[i] != '=' and 


                string[i] != '-') : 


            operands[k] += string[i];  


        else :  


            operators[k] = string[i];  


  


            # Evaluation of 1st operator  


            if (k == 1) :  


                if (operators[k - 1] == '+') :  


                    ans += int(operands[k - 1]) + int(operands[k]);  


  


                if (operators[k - 1] == '-') : 


                    ans += int(operands[k - 1]) - int(operands[k]);  


  


            # Evaluation of 2nd operator  


            if (k == 2) : 


                if (operators[k - 1] == '+') : 


                    ans1 += ans + int(operands[k]);  


  


                if (operators[k - 1] == '-') : 


                    ans1 -= ans - int(operands[k]);  


              


  


            # Evaluation of 3rd operator  


            if (k == 3) :  


                if (operators[k - 1] == '+') : 


                    ans2 += ans1 + int(operands[k]);  


  


                if (operators[k - 1] == '-') : 


                    ans2 -= ans1 - int(operands[k]);  


            k += 1


  


    # If the LHS result is equal to the RHS  


    if (ans2 == int(operands[4])) : 


        return True;  


    else : 


        return False;  


  


  


# Driver code  


if __name__ == "__main__" :  


  


    string = "2 + 5 + 3 + 1 = 11";  


    if (isValid(string)) : 


        print("Valid");  


    else : 


        print("Invalid");  


          


# This code is contributed by Ryuga 



















                        chevron_right







                        filter_none











Output:


Valid






          
          
          
          

            

    

        My Personal Notes
        arrow_drop_up
    

    

        
        

            
            
        

    


Recommended Posts:
Naman_Garg
Check out this Author's contributed articles.
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on  the "Improve Article" button below.


Improved By :  AnkitRai01


      
      
      
      

      

      
					
		

    Article Tags : 
C++ Programs
Strings

           	
Practice Tags : 
Strings

        

         

         
 
         
        Be the First to upvote.

                

        



        
        
        
        
        

    

            

            0
            

            

                             No votes yet.
                    

            
            
            
            
            
        

        
        

        

        

        

        

        

        


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.