157. Read N Characters Given Read4

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.

一刷
题解：就是将一个很大的文件读取函数变成每4个4个的读取（读函数已写好）， 并返回总共读到的字符数目

/* 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[] buf4 = new char[4];
        int offset = 0;
        
        while(true){
            int size = read4(buf4);
            for(int i=0; i<size && offset<n; i++){
                buf[offset++] = buf4[i];
            }
            if(size == 0 || offset == n) return offset;
        }
    }
}

二刷
同上

/* 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[] buf4 = new char[4];
        int offset = 0;
        while(true){
            int size = read4(buf4);
            for(int i=0; i<size && offset<n; i++){
                buf[offset++] = buf4[i];
            }
            if(size == 0 || offset==n) return offset;
        }
    }
}