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check_balance

Language/Type: PHP stack collections string

Write a function named check_balance that accepts a string of source code and uses an array 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
check_balance("if (a(4) > 9) { foo(a(2)); }")     // returns -1 because balanced
check_balance("for (i=0;i<a(3};i++) { foo{); )")  // returns 14 because } out of order
check_balance("while (true) foo(); }{ ()")        // returns 20 because } doesn't match any {
check_balance("if (x) {")                         // returns 9 because { is never closed

Constraints: Use a single array stack as auxiliary storage.

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

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