Read N Characters Given Read4 I & II

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 may be called only once.

 public class Solution extends Reader4 {
     public int read(char[] buf, int n) {
         int index = ;
         char[] tmp = new char[]; // temp buffer

         while (index < n) {
             int count = read4(tmp);
             count = Math.min(count, n - index);
             for (int i = ; i < count; i++) {
                 buf[index++] = tmp[i];
             }
             if (count < ) {
                 return index;
             }
         }
         return index;
     }
 }

 public class Solution extends Reader4 {
     public int read(char[] buf, int n) {
         boolean eof = false;
         int charsRead = ;
         char[] buf4 = new char[];

         while (!eof && charsRead < n) {
             int size = read4(buf4);
             if (size < ) {
                 eof = true;
             }

             if (charsRead + size > n) {
                 size = n - charsRead;
             }

             System.arraycopy(buf4, , buf, charsRead, size);
             charsRead += size;
         }
         return charsRead;
     }
 }

Read N Characters Given Read4 II - Call multiple times

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 may be called multiple times.

分析：

 public class Solution extends Reader4 {
     char[] buffer = new char[];
     int bufferSize = , prevIndex = ;

     public int read(char[] buf, int n) {
         int index = ;
         while (index < n) {
             if (prevIndex < bufferSize) {
                 buf[index++] = buffer[prevIndex++];
             } else {
                 bufferSize = read4(buffer);
                 prevIndex = ;
                 if (bufferSize == ) { break; }
             }
         }
         return index;
     }
 }

 public class Solution extends Reader4 {
     private char[] buffer = new char[];
     int offset = , bufsize = ;

     public int read(char[] buf, int n) {
         int readBytes = ;
         boolean eof = false;
         while (!eof && readBytes < n) {
             int sz = (bufsize > ) ? bufsize : read4(buffer);
             if (bufsize ==  && sz < ) eof = true;
             int bytes = Math.min(n - readBytes, sz);
             System.arraycopy(buffer, offset, buf,  readBytes, bytes);
             offset = (offset + bytes) % ;
             bufsize = sz - bytes;
             readBytes += bytes;
         }
         return readBytes;
     }
 }