Solution 1 simulation

• t-complexity: $O(logn)$ n is num's value, i /= 1000, so it's log

• s-complexity: $O(logn)$

In English three words a group, for num <= 2^ 31 - 1, possible range is

• Billion

• Million

• Thousand

And leading these words with [0, 999]

Use a function num2str to convert nubmer bellow 999

• x >= 100: Need ??? Hundred

• x >= 20: Need ??? XXX-ty

• x < 20: Show simple words