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

這題和157一樣，提供read4 API，要寫read function。不同在於read可以被call很多次。

• idea:  大致上和157相同，只差在eof要變成class的member， 並將一個queue加入class member，用來存read4後沒有寫入buf的character。 開始讀檔之前，先讀取queue裡面的字元，並在read4之後把沒存進buf的字元放進queue

• pseudocode:

  read char from queue first
  
  while file not finish, and total < n,
      read4 into tmp,
      add 4 to total.
      if total read after read4 < n
          put into buffer
      else
          remainder = n-(total-4)
          total = n
          put remainder char into buf
          and put count-remainder char into queue
  
  return total
  

• code:

  /* The read4 API is defined in the parent class Reader4.
        int read4(char[] buf); */
  
  public class Solution extends Reader4 {
      /**
       * @param buf Destination buffer
       * @param n   Maximum number of characters to read
       * @return    The number of characters read
       */
  
      //safe the characters that doesn't read into buf in last call
      Queue<Character> queue = new LinkedList<>();
      boolean eof = false;
  
      public int read(char[] buf, int n) {
          int total = 0;
          int idx = 0;
  
          //clear queue first
          while(!queue.isEmpty() && total < n){
              char c = queue.peek();
              queue.poll();
              buf[idx++] = c;
              total++;
          }
  
          while(!eof && total<n){
              char[] tmp = new char[4];
              int count = read4(tmp);
  
              if(count < 4) eof = true;
  
              total+=count;
              if(total < n){
                  for(int i=0; i<4; i++){
                      buf[idx++] = tmp[i];
                  }
              }else{
                  int remainder = n-(total-count);
                  total = n;
                  int i=0;
                  for(i=0; i<remainder; i++){
                      buf[idx++] = tmp[i];
                  }
                  //put the numbers left in tmp into queue
                  while(i<4 && remainder < count){
                      queue.offer(tmp[i]);
                      i++;
                      remainder++;
                  }
              }
          }
  
          return total;
      }
  }