158. Read N Characters Given Read4 II - Call multiple times

Read N Characters Given Read4 II - Call multiple times

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 may be called multiple times.

Solution

/* The read4 API is defined in the parent class Reader4.
      int read4(char[] buf); */

public class Solution extends Reader4 {
    char[] last;
    int startIndex = 4;
    int readCount = 4;


    public int read(char[] buf, int n) {
        int index = 0;

        while (startIndex < readCount && index <n){
            buf[index] = last[startIndex];
            index ++;
            startIndex ++;
        }

        while (index < n) {
            char[] temp = new char[4];
            int readCount = read4(temp);

            if (readCount == 0) {
                break;
            }

            int i = 0;
            while (i < readCount) {
                if (index < n) {
                    buf[index] = temp[i];
                    index++;
                } else {
                    break;
                }
                i ++;
            }

            last = temp;
            startIndex = i;
            this.readCount = readCount;
        }

        return index;
    }
}