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.

每次只读4个，因此不能用buf直接给read4. 因为如果读五个，直接传buf的时候，读第五个地方的时候会覆盖第一个位置

  public int read(char[] buf, int n) {  
     int count = 0;  
     while(count < n){  
       char[] tmp = new char[4];  
       int c= read4(tmp);  
       for(int j = 0; j < c && count < n; j++){  
         buf[count++] = tmp[j];  
       }  
       if(c < 4) break;   
     }  
     return count;  
   }