158. Read N Characters Given read4 II - Call Multiple Times
Explanation
To solve this problem, we need to implement a method int read(char[] buf, int n) that reads data from a file using the read4 API multiple times. The read4 API reads 4 characters at a time and returns the number of characters read. The read method should return the total number of characters read.
We can maintain an internal buffer to store the characters read by read4 but not yet consumed by the read method. We use two pointers bufPtr and bufCnt to keep track of the current position in the buffer and the total number of characters in the buffer respectively.
The algorithm works as follows:
- If
bufPtrreaches the end of the buffer, we read more characters from the file usingread4and refill the buffer. - We copy characters from the internal buffer to the output buffer
bufuntil either we reachncharacters or we exhaust all characters in the internal buffer. - If we reach the end of the file or
ncharacters are read, we return the total number of characters read.
public class Solution extends Reader4 {
private char[] buffer = new char[4];
private int bufPtr = 0;
private int bufCnt = 0;
public int read(char[] buf, int n) {
int total = 0;
boolean eof = false;
while (!eof && total < n) {
if (bufPtr == 0) {
bufCnt = read4(buffer);
}
if (bufCnt == 0) {
eof = true;
}
while (total < n && bufPtr < bufCnt) {
buf[total++] = buffer[bufPtr++];
}
if (bufPtr == bufCnt) {
bufPtr = 0;
}
}
return total;
}
}Code Editor (Testing phase)
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