Drawing

Chef has a string $S$. A substring of $S$ is obtained by removing zero or more characters from the beginning and/or end of $S$. For each $L$ ($1 \le L \le |S|$): - $K$ times, Chef wants to choose a substring of $S$ with length $L$ uniformly randomly and independently. - Find the probability that all these $K$ substrings will be pairwise distinct. It can be proved that this probability can be exp