# 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

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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 on operands and operands and store it in ans.
• Then perform the seconds arithmetic operation i.e. operators on ans and operators and so on.
• Finally, compare the ans calculated with the last operand i.e. operands. 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 ` `using` `namespace` `std; ` ` `  `// Function that returns true if the equation is valid ` `bool` `isValid(string str) ` `{ ` `    ``int` `k = 0; ` `    ``string operands = ``""``; ` `    ``char` `operators; ` `    ``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)) ` `        ``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; ` `} `

## 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 `

Output:

```Valid
```

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