Formatted question description: https://leetcode.ca/all/158.html
157 Read N Characters Given Read4 The API: int read4(char *buf) reads 4 characters at a time from a file. The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file. By using the read4 API, implement the function int read(char *buf, int n) that reads n characters from the file. Note: The read function will only be called once for each test case.
Two variables readPos and writePos are used to record the position of reading and writing, i starts looping from 0 to n,
- If the read and write positions are the same at this time, call the read4 function, assign the result to writePos, and set readPos to zero,
- If writePos is zero, indicating that there is nothing in buf, return the current coordinate i. Then use the readPos position of the built-in buff variable to overwrite the i position of the input string buf,
- If the traversal is completed, return n