titleCase
Return the provided string with the first letter of each word capitalized. Make sure the rest of the word is in lower case.
Examples
titleCase('I'm a little tea pot') → 'I'm A Little Tea Pot'
Starter code
function titleCase(str) {
}
Complexity of the optimal solution
Time O(n), space O(n). The operations `toLowerCase`, `split`, `map`, and `join` all process the entire string or resulting arrays. The time and space required are proportional to the length of the input string (n).