158 Read N Characters Given Read4 II - Call multiple times

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 theread4API, implement the functionint read(char *buf, int n)that readsncharacters from the file.

Note:
Thereadfunction 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 ""

Understand the diff between 1 and 2

/* The read4 API is defined in the parent class Reader4.
      int read4(char[] buf); */

public class Solution extends Reader4 {
    /**
     * @param buf Destination buffer
     * @param n   Maximum number of characters to read
     * @return    The number of characters read
     */
    private int tempPtr = 0;
    private int count = 0;
    private char[]temp = new char[4];  //global array
    public int read(char[] buf, int n) {//READ MULTIPLE TIMES, MEANS EVERYTIME, INDEX = 0 AND WRITE TO BUF
        int index = 0;
        while (index < n) {
            if (tempPtr == 0) {//temp is empty
                count = read4(temp);//use counter to count 
            }
            if (count == 0) {
                break;//nothing to read
            }
            //write
            while (index < n && tempPtr < count) {
                buf[index++] = temp[tempPtr++];
            }
            if (tempPtr == count ){//means you have written everything from temp to buf
                tempPtr = 0;
            }
        }
        return index;
    }
}