157.Read N Characters Given Read4

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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.

Solution

    public int reads(char[] buf, int n) {
        char[] internal = new char[4];
        int offset = 0;
        while (true) {
            int count = read4(internal);
            for (int i = 0; i < count && offset < n; i++) {
                buf[offset++] = internal[i];
            }
            if (offset == n || count == 0) {
                break;
            }
        }
        return offset;
    }