Read N Characters Given Read4
AppleThe problem
You are given a file and a function read4 that reads up to 4 consecutive characters from the file into a buffer. Your task is to implement a function read that reads up to n characters using read4.
read4 Function Definition: def read4(buf4: List[str]) -> int:
- Functionality: Reads up to 4 characters from the file into buf4 and returns the number of characters actually read.
- File Pointer: read4 maintains its own internal file pointer, similar to FILE *fp in C.
Example Behavior of read4 file = "abcde" buf4 = [""] * 4
read4(buf4) # Returns 4, buf4 = ["a", "b", "c", "d"], file pointer moves to "e" read4(buf4) # Returns 1, buf4 = ["e"], file pointer reaches EOF read4(buf4) # Returns 0, buf4 = [], file pointer remains at EOF
Implementing read Function Your task is to implement the read function: def read(buf: List[str], n: int) -> int:
Parameters:
-
buf: A destination buffer to store the read characters.
-
n: The number of characters to read. Returns:
-
The actual number of characters read from the file. Constraints:
-
You cannot access the file directly; you can only use read4.
-
The read function is called only once per test case.
-
buf has enough space for n characters.
**Input: **file = "abc", n = 4 Output: 3 Explanation: The file has only "abc". Since n=4, we try to read 4 characters but can only get 3.
**Input: **file = "abcde", n = 5 Output: 5 Explanation: The file contains 5 characters, and we request 5, so all characters are read.
**Input: **file = "abcdABCD1234", n = 12
- 1 ≤ file.length ≤ 500
- 1 ≤ n ≤ 1000
- file consists only of English letters and digits.
cpp
class Solution {
public:
/**
* @param buf Destination buffer
* @param n Number of characters to read
* @return The number of actual characters read
*/
int read(char *buf, int n) {
// Your code goes here
}
};java
class Solution extends Reader4 {
/**
* @param buf Destination buffer
* @param n Number of characters to read
* @return The number of actual characters read
*/
public int read(char[] buf, int n) {
// Your code goes here
}
}python
class Solution(Reader4):
"""
Reads 'n' characters from the file using the read4 method.
:param buf: Destination buffer (list of characters)
:param n: Number of characters to read
:return: Number of actual characters read
"""
def read(self, buf, n):
# Your code goes herejavascript
class Solution extends Reader4 {
/**
* @param {string[]} buf Destination buffer
* @param {number} n Number of characters to read
* @return {number} The number of actual characters read
*/
read(buf, n) {
// Your code goes here
}
}csharp
class Solution : Reader4
{
/**
* @param buf Destination buffer
* @param n Number of characters to read
* @return The number of actual characters read
*/
public int Read(char[] buf, int n)
{
// Your code goes here
}
}go
func Read(buf []byte, n int) int {
//your code goes here
}Stuck? Show a way to structure it+
- 01Keep a temporary buffer of four characters.
- 02Call read4 while destination space remains.
- 03Copy only the smaller of count and remaining.
- 04Stop on EOF or after n copied characters.
- 05Discard excess only because this version is called once.
Reference answer
Then expect these follow-ups
How would you redesign this for multiple read calls?
Tests: follow-up reasoning
Why must read4's return count control the copy loop?
Tests: correctness reasoning
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