max_profit() {
    local -n _a="$1"
    local _price=${_a[0]} _profit=0 _v
    for _v in "${_a[@]}"; do
        (( _v < _price )) && _price=$_v
        local _cur=$(( _v - _price ))
        (( _cur > _profit )) && _profit=$_cur
    done
    echo "$_profit"
}