Description
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.
**Example 1: **
Given buf = "abc"
read("abc", 1) // returns "a"
read("abc", 2); // returns "bc"
read("abc", 1); // returns ""
**Example 2: **
Given buf = "abc"
read("abc", 4) // returns "abc"
read("abc", 1); // returns ""
Solution
Buffer
添加一个缓冲区tmp[]。
/* The read4 API is defined in the parent class Reader4.
int read4(char[] buf); */
public class Solution extends Reader4 {
private char[] tmp = new char[4];
private int pos = 0;
private int count = 0;
/**
* @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) {
int i = 0;
while (i < n) {
if (pos == 0) { // tmp is eat up
count = read4(tmp);
}
if (count == 0) { // file ended
break;
}
buf[i++] = tmp[pos++];
if (pos == count) {
pos = 0;
}
}
return i;
}
}
