Your input "Hi (there)" is not valid input for this kata. Input consists of only ({[]}) characters

Although inefficient as you need to iterate over the entire vector, it's beautiful!

wow

Very similar to mine, except I prefer only to use arrow functions for super simple one-liner functions.

Love this. One line, easy to read, and probably more efficient than most of the others.

Great solution with explanation how it works.

It does work - it passes the Kata tests. The Kata description could probably have been more explicit taht the string will only contain the characters '(){}[]'.

This won't work correctly on arrays with only negative values (it returns -1 on [-1,-1] for example)

Nice and simple. I'd prefer a for_each instead of the loop, though.