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checkBalance

Language/Type: C++ stack collections STL
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Write a function named checkBalance that accepts a string of source code and uses a stack to check whether the braces/parentheses are balanced. Every ( or { must be closed by a } or ) in the opposite order. Return the index at which an imbalance occurs, or -1 if the string is balanced. If any ( or { are never closed, return the string's length.

Here are some example calls: 

//    index   0123456789012345678901234567890
checkBalance("if (a(4) > 9) { foo(a(2)); }")         // returns -1 because balanced
checkBalance("for (i=0;i<a(3};i++) { foo{); )")   // returns 14 because } out of order
checkBalance("while (true) foo(); }{ ()")            // returns 20 because } doesn't match any {
checkBalance("if (x) {")                             // returns 8 because { is never closed

Constraints: Use a single stack as auxiliary storage.

Function: Write a C++ function as described, not a complete program.

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