157. Read N Characters Given Read4

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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.

解法1：

C++

1

Java

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/* 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) {
        char[] buffer = new char[4];
        int pos = 0;
        while (pos < n) {
            int read = read4(buffer);
            for (int i = 0; i < read && pos < n; i++) {
                buf[pos++] = buffer[i];
            }
            if (read == 0) {
                break;
            }
        }
        return pos;
    }
}