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# 157 Read N Characters Given Read4 – Easy

\#157 LeetCode Java: Read N Characters Given Read4 – Easy

#### Problem:

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.

#### Thoughts

This is an easy question but we need to get the meaning of requirements correct. At the beginning, I thought read4 function is reading characters from buf. So does the function read. But that’s not correct.

The meaning here is that read4() function will read 4 characters at a time from a file and then put the characters that has been read into this buf variable. So read() function is reading at most n characters from a file ( we don’t know what file and how it’s reading from the file), and put x characters into char\[] buf.

#### Solutions:

```java
/* 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 offset = 0;
        char[] buf4 = new char[4];
        int buf4index = 0;
        int buf4size = 0;
        while(offset < n) {
            if (buf4index >= buf4size) {
                buf4size = read4(buf4);
                buf4index = 0;
                if (buf4size == 0) {
                    break;
                }
            }
            buf[offset] = buf4[buf4index];
            offset ++;
            buf4index ++;
        }
        return offset;
    }
}
```