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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