# Question

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
that reads n characters from the file.

Note:
The read function will only be called once for each test case.



# Algorithm

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

Java