_158.java

package com.fishercoder.solutions;

/**
 * 158. 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.
 *
 * Example 1:
 * Given buf = "abc"
 * read("abc", 1) // returns "a"
 * read("abc", 2); // returns "bc"
 * read("abc", 1); // returns ""
 *
 * Example 2:
 * Given buf = "abc"
 * read("abc", 4) // returns "abc"
 * read("abc", 1); // returns ""
 */
public class _158 {

    public static class Solution1 {
        /**
         * @param buf Destination buffer
         * @param n   Maximum number of characters to read
         * @return The number of characters read
         */
        private int buffPtr = 0;
        private int buffCnt = 0;
        private char[] buff = new char[4];

        public int read(char[] buf, int n) {
            int ptr = 0;
            while (ptr < n) {
                if (buffPtr == 0) {
                    buffCnt = read4(buff);
                }
                if (buffCnt == 0) {
                    break;
                }
                while (ptr < n && buffPtr < buffCnt) {
                    buf[ptr++] = buff[buffPtr++];
                }
                if (buffPtr >= buffCnt) {
                    buffPtr = 0;
                }
            }
            return ptr;
        }

        //This is a fake method to make IDE happy.
        private int read4(char[] buff) {
            return 1;
        }
    }
}