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check_balance

Language/Type: Python list collections string

Write a function named check_balance that accepts a string of source code and uses a list 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=0i&lta(3}i += 1): foo{) )")   # returns 14 because } out of order
check_balance("while True) foo() }{ ()"         # returns 20 because } doesn't match any {
check_balance("if x:")                          # returns 8 because { is never closed

Constraints: Use a single stack as auxiliary storage.

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

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