資訊專(zhuān)欄INFORMATION COLUMN
Problem
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
public class Solution extends Reader4 {
/**
* @param buf Destination buffer
* @param n Maximum number of characters to read
* @return The number of characters read
*/
int count = 0; //count the length of data retrieved by read4()
int index = 0; //record the position of data consumed by read()
char[] data = new char[4];
public int read(char[] buf, int n) {
int i = 0;
while (i < n) {
//get new data with read4 api
if (index == 0) count = read4(data);
//if no new data, break
if (count == 0) break;
//consume data
while (i < n && index < count) {
buf[i++] = data[index++];
}
//all existing data consumed, restart with index = 0
if (index >= count) index = 0;
}
//return the length of data read
return i;
}
}
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