用 Read4 读取 N 个字符 II - 多次调用

/*
 * Problem: Given an API int read4(char[] buf), read4 reads 4 characters at a time from a file.
 * The return value is the actual number of characters read. Implement a method int read(char[] buf, int n)
 * that uses this API to read n characters.
 * 
 * Approach:
 * 1. Use a buffer to store the temporary characters read by read4.
 * 2. Use Java Streams to manage and process the reading process efficiently.
 * 3. Loop until we have read the desired number of characters or there are no more characters to read.
 * 4. Each time, call read4 and copy the characters to the final buffer.
 * 5. Adjust the count to ensure we do not read more than required.
 */
import java.util.stream.IntStream;
 
public class Solution extends Reader4 {
    private char[] buffer = new char[4];
    private int bufferPtr = 0;
    private int bufferCount = 0;
 
    public int read(char[] buf, int n) {
        int totalRead = 0;
 
        while (totalRead < n) {
            if (bufferPtr == bufferCount) {
                bufferCount = read4(buffer);
                bufferPtr = 0;
                if (bufferCount == 0) break; // End of file reached
            }
 
            while (totalRead < n && bufferPtr < bufferCount) {
                buf[totalRead++] = buffer[bufferPtr++];
            }
        }
 
        return totalRead;
    }
}