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: InvalidInput: 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++
// 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; } |
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Python3
# 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 |
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Output:
Valid
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