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LeetCode

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Problem

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.

Code

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

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 index = 0;
        // 直到把buf填满或者读完了全部的字符
        while(true){
            int count = read4(temp);
            count = Math.min(count, n - index);
            for(int i = 0; i < count; i++){
                buf[index++] = temp[i];
            }

            if(index == n || count < 4) return index;
        }
    }
}