Practice/Google/Leetcode 157. Read N Characters Given Read4

Leetcode 157. Read N Characters Given Read4

CodingMust

Problem

You are working with a file reading system that provides a low-level API called read4. This API reads up to 4 characters at a time from a file into a temporary buffer and returns the actual number of characters read.

Your task is to implement a higher-level read function that uses read4 to read exactly n characters (or fewer if the end of file is reached) into a destination buffer.

The read4 API signature:

• Input: buf4 - a temporary buffer array that can hold 4 characters
• Output: An integer representing the actual number of characters read (0 to 4)
• Behavior: Reads the next available characters from the file (up to 4) and places them in buf4. Returns the count of characters actually read. Returns 0 when the end of file is reached.

Requirements

1. Implement the read(buf, n) function that reads n characters into the destination buffer buf
2. Use only the provided read4 API to access the file
3. Handle cases where the file has fewer than n characters
4. Handle cases where n is not a multiple of 4
5. Return the actual number of characters successfully read

Constraints

• 0 ≤ n ≤ 10,000
• The file contains only ASCII characters
• You can assume buf has enough space to hold n characters
• You must use the read4 API and cannot directly access the file

Examples

Example 1:

` File content: "abcdefghij" n = 5

Process:

• First read4: reads "abcd" (4 chars)
• Second read4: reads "e" from "efgh" (need only 1 more)
• Result: buf = ['a','b','c','d','e']

Output: 5 `

Example 2:

` File content: "abc" n = 10

Process:

• First read4: reads "abc" (3 chars, EOF reached)
• Result: buf = ['a','b','c']

Output: 3 Explanation: Only 3 characters exist, so only 3 can be read `

Example 3:

` File content: "abcdefgh" n = 8

Process:

• First read4: reads "abcd" (4 chars)
• Second read4: reads "efgh" (4 chars)
• Result: buf = ['a','b','c','d','e','f','g','h']

Output: 8 `

Example 4:

` File content: "" n = 1

Process:

• First read4: reads nothing (0 chars, EOF)

Output: 0 `