LeetCode Read N Characters Given Read4 II

原题链接在这里：https://leetcode.com/problems/read-n-characters-given-read4-ii-call-multiple-times/

题目：

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.

题解：

需要多次调用，用queue来保存前一次调用read4没用完的数据.

read时先用queue中的数据添加到buf中，若是不够再call read4.

在读够n个char后若是read4Buff中还有可用数据，加到queue中.

Note: declear rest first, but not use i < n - readSum in the while condidtion since readSum is changing.

Time Complexity: read, O(n).

Space: O(1). queue的大小不会超过4.

AC Java:

 /**

  * The read4 API is defined in the parent class Reader4.

  *     int read4(char[] buf);

  */

 public class Solution extends Reader4 {

     LinkedList<Character> que = new LinkedList<>();

     /**

      * @param buf Destination buffer

      * @param n   Number of characters to read

      * @return    The number of actual characters read

      */

     public int read(char[] buf, int n) {

         int readSum = 0;

         // 先用queue中剩余的上次结果加到buf中

         while(readSum < n && !que.isEmpty()){

             buf[readSum++] = que.poll();

         }

         // 若是不够再调用read4 API

         boolean eof = false;

         char [] temp = new char[4];

         while(!eof && readSum < n){

             int count = read4(temp);

             eof = count < 4;

             int rest = n-readSum;

             int i = 0;

             while(i < count && i < rest){

                 buf[readSum++] = temp[i++];

             }

             // 把当前read4Buff中没有读的有用char加到queue中

             if(i == rest){

                 while(i < count){

                     que.add(temp[i++]);

                 }

             }

         }

         return readSum;

     }

 }

类似Read N Characters Given Read4.

巴特西

LeetCode Read N Characters Given Read4 II - Call multiple times

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