Suppose, for a stock, we have a series of n daily price quotes, the span
of the stock's price on a given day is defined as the maximum number of
consecutive days just before the given day, for which the price of the
stock on the current day is less than or equal to its price on the given
day.
Let, Price (i) = price of the stock on day "i".
Then, Span (i) = max {k : k >= 0 and Price (j) <= Price (i) for j = i - k, .., i}
Thus, if Price (i-1) > Price (i), then Span (i) = 0.
Time Complexity: O(n)
Space Complexity: O(n) for stack.