_158.java

package com.fishercoder.solutions;

/**
 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 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 ""
 */
public class _158 {

  public static class Solution1 {
    /**
     * @param buf Destination buffer
     * @param n   Maximum number of characters to read
     * @return The number of characters read
     */
    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;
    }

    //This is a fake method to make IDE happy.
    private int read4(char[] buff) {
      return 1;
    }
  }
}