[LeetCode] 157. Read N Characters Given Read4

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 will only be called once for each test case.

Thought process:

Use a temporary buffer of size 4. Copy from the temporary buffer to buf based on n. Break out of the loop if I reached end of file.

Solution:

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/* The read4 API is defined in the parent class Reader4. int read4(char[] buf); */ public class Solution extends Reader4 { /** * @param buf Destination buffer * @param n Maximum number of characters to read * @return The number of characters read */ public int read(char[] buf, int n) { char[] temp = new char[4]; int total = 0; while (true) { int read = Math.min(n - total, read4(temp)); if (read == 0) { break; } for (int i = 0; i < read; i++) { buf[total + i] = temp[i]; } total += read; } return total; } }

Time complexity: O(min(n, file)).