题目内容 John likes to travel. He has visited a lot of cities over many years. Whenever he visits a city, he takes a few photos and saves them on his computer. Each photo has a name with an extension ("
题的内容 Task 1You are given a string letters made of N English letters. Count the number of different letters that appear in both uppercase and lowercase where all lowercase occurrences of the given l
题目 Task 3There are N patients (numbered from 0 to N-1) who want to visit the doctor. The doctor has S possible appointment slots, numbered from 1 to S. Each of the patients has two preferences. Pat