flags() {
    local -n _a="$1"
    local _size=${#_a[@]}
    local -a _peak _nxt
    _peak[0]=0
    local _i
    for ((_i = 1; _i < _size; _i++)); do
        local _right=0
        (( _i + 1 < _size )) && _right=${_a[_i+1]}
        if (( _a[_i-1] < _a[_i] && _a[_i] > _right )); then _peak[_i]=1; else _peak[_i]=0; fi
    done
    _nxt[_size-1]=-1
    for ((_i = _size - 2; _i >= 0; _i--)); do
        if (( _peak[_i] )); then _nxt[_i]=$_i; else _nxt[_i]=${_nxt[_i+1]}; fi
    done
    _i=1
    local _result=0
    while (( _i * (_i - 1) <= _size )); do
        local _pos=0 _num=0
        while (( _pos < _size && _num < _i )); do
            _pos=${_nxt[_pos]}
            if (( _pos == -1 )); then break; fi
            ((_num++))
            _pos=$(( _pos + _i ))
        done
        ((_i++))
        (( _num > _result )) && _result=$_num
    done
    echo "$_result"
}