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.
Solution:
1 /* The read4 API is defined in the parent class Reader4. 2 int read4(char[] buf); */ 3 4 public class Solution extends Reader4 { 5 char[] tempBuf = new char[4]; 6 int offset = 4; 7 int maxLen = 4; 8 9 /** 10 * @param buf 11 * Destination buffer 12 * @param n 13 * Maximum number of characters to read 14 * @return The number of characters read 15 */ 16 public int read(char[] buf, int n) { 17 int ind = 0; 18 while (offset < maxLen && ind < n) { 19 buf[ind++] = tempBuf[offset++]; 20 } 21 if (maxLen < 4) return ind; 22 23 ind = readFile(buf, ind, n); 24 return ind; 25 } 26 27 public int readFile(char[] buf, int ind, int n) { 28 int num = 4; 29 while (num == 4 && ind < n) { 30 num = read4(tempBuf); 31 int end = Math.min(num, n - ind); 32 for (offset = 0; offset < end; offset++) { 33 buf[ind++] = tempBuf[offset]; 34 } 35 } 36 maxLen = num; 37 return ind; 38 } 39 }