158. Read N Characters Given Read4 II - Call multiple times

158. Read N Characters Given Read4 II - Call multiple times




Given buf = "abc"
read("abc", 1) // returns "a"
read("abc", 2); // returns "bc"
read("abc", 1); // returns ""
Example 2: 

Given buf = "abc"
read("abc", 4) // returns "abc"
read("abc", 1); // returns ""

   

    private int buffPtr = 0;
    private int buffCnt = 0;
    private char[] buff = new char[4];
    public int read(char[] buf, int n) {
        int ptr = 0;
        while (ptr < n) {
            if (buffPtr == 0) {
                buffCnt = read4(buff);
            }
          
            if (buffCnt == 0) break;
          
            while (ptr < n && buffPtr < buffCnt) {
                buf[ptr++] = buff[buffPtr++];
            }
          
            if (buffPtr >= buffCnt){
              buffPtr = 0;
            }
        }
        return ptr;
    }
I used buffer pointer (buffPtr) and buffer Counter (buffCnt)
  to store the data received
in previous calls. In the while loop,
if buffPtr reaches current buffCnt, it will be set
as zero to be ready to read new data.

 

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 may be called multiple times.

Example 1: 

Given buf = "abc"
read("abc", 1) // returns "a"
read("abc", 2); // returns "bc"
read("abc", 1); // returns ""

Example 2: 

Given buf = "abc"
read("abc", 4) // returns "abc"
read("abc", 1); // returns ""