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.

Examples

Example 1

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Input:
"filetestbuffer"
read(6)
read(5)
read(4)
read(3)
read(2)
read(1)
read(10)
Output:
6, buf = "filete"
5, buf = "stbuf"
3, buf = "fer"
0, buf = ""
0, buf = ""
0, buf = ""
0, buf = ""

Example 2

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Input:
"abcdef"
read(1)
read(5)
Output:
1, buf = "a"
5, buf = "bcdef"

Solution

Method 1 - String Enumeration

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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 ptr = 0;
    private int count = 0;
    private char[] buff = new char[4];
    public int read(char[] buf, int n) {
        int i = 0;
        while (i < n) {
            if (ptr == 0) {
                count = read4(buff);
            }
            if (count == 0) break;
            while (i < n && ptr < count) {
                buf[i++] = buff[ptr++];
            }
            if (ptr >= count) ptr = 0;
        }
        return i;
    }
}