157. Read N Characters Given Read4 - Easy

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.

Example 1:

Input: buf = "abc", n = 4
Output: "abc"
Explanation: The actual number of characters read is 3, which is "abc".

Example 2:

Input: buf = "abcde", n = 5 
Output: "abcde"

Note:
The read function will only be called once for each test case.

 

time: O(N), space: O(1)

/* 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[] tmp = new char[4];
        boolean endOfFile = false;
        int total = 0;
        
        while(total < n && endOfFile == false) {
            int cur = read4(tmp);
            if(cur != 4)
                endOfFile = true;
            cur = Math.min(n - total, cur);
            for(int i = 0; i < cur; i++) {
                buf[total++] = tmp[i];
            }
        }
        return total;
    }
}

 

 

reference: https://leetcode.com/problems/read-n-characters-given-read4/discuss/49496/Another-accepted-Java-solution