Balanced brackets with a stack

Problem

Check whether the brackets (), [] and {} in each line of text are balanced. All other characters are ignored.

Input. An integer n, then n lines of text (a line may be empty).

Output. For each line, print its number (starting at 1), a colon and a space, then either Balanced or Unbalanced at index i, where i (0-based) is:

the index of the first closing bracket that has no matching opener (the stack is empty, or its top is a different kind of bracket); or
if the line ends with brackets still open, the index of the most recently opened bracket that was never closed.

Use a Deque<Integer> as a stack of the indices of open brackets (push, pop, peek).

Input:
4
([]{})
(]
a[i] = (b + c) * {d};
((

Output:
1: Balanced
2: Unbalanced at index 1
3: Balanced
4: Unbalanced at index 1

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