157. Read N Characters Given Read4

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.

Solution

/* 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
     */
    public int read(char[] buf, int n) {
        int index = 0;
        while (index < n) {
            char[] temp = new char[4];
            int readCount = read4(temp);

            if (readCount == 0) {
                break;
            }

            for (int i = 0; i < readCount; i++) {
                if (index < n) {
                    buf[index] = temp[i];
                    index++;
                } else {
                    break;
                }
            }
        }

        return index;
    }
}