largest_string() {
    local _s=$1
    local -a _c
    local _i _len=${#_s}
    for ((_i = 0; _i < _len; _i++)); do _c[_i]=${_s:_i:1}; done
    local _cur=""
    for ((_i = _len - 1; _i >= 0; _i--)); do
        _cur="${_c[_i]}${_cur}"
        if (( ${#_cur} == 3 )); then
            if [[ "$_cur" == "abb" ]]; then
                _c[_i]="b"; _c[_i+1]="a"; _c[_i+2]="a"
                if [[ -n "${_c[_i+4]:-}" && "${_c[_i+4]}" == "b" ]]; then
                    _i=$(( _i + 4 + 1 ))
                elif [[ -n "${_c[_i+3]:-}" && "${_c[_i+3]}" == "b" ]]; then
                    _i=$(( _i + 3 + 1 ))
                elif [[ "${_c[_i+2]}" == "b" ]]; then
                    _i=$(( _i + 2 + 1 ))
                fi
            fi
            if [[ "${_c[_i+1]}" == "b" ]]; then
                _i=$(( _i + 1 + 1 ))
            else
                ((_i++))
            fi
            _cur=""
        fi
    done
    local _out=""
    for ((_i = 0; _i < _len; _i++)); do _out="${_out}${_c[_i]}"; done
    echo "$_out"
}