Leetcode-Read N Characters Given Read4 II

 1 /* The read4 API is defined in the parent class Reader4.
 2       int read4(char[] buf); */
 3 
 4 public class Solution extends Reader4 {
 5     /**
 6      * @param buf Destination buffer
 7      * @param n   Maximum number of characters to read
 8      * @return    The number of characters read
 9      */
10 
11     public char[] carry;
12     public int index;
13 
14     public int read(char[] buf, int n) {
15         int left = n;
16  
17         //Put carry over into buf, and destroy the carry over array!
18         if (carry!=null){
19             while (left>0 && index<carry.length){
20                 buf[n-left]=carry[index];
21                 left--;
22                 index++;
23             }
24             if (index>=carry.length){
25                 carry=null;
26                 index=-1;
27             }
28         }
29 
30         char[] tempBuf = new char[4];
31         while (left>0){
32             int num = read4(tempBuf);
33             //if the read number is larger then what we need, then we just put the left number of chars into buf.
34             //And put the rest chars into carry array.
35             if (num>left){
36                 carry = new char[num-left];
37                 for (int i=left;i<num;i++)
38                     carry[i-left] = tempBuf[i];
39                 index = 0;
40             }
41 
42             int end = Math.min(num,left);
43             for (int i=0;i<end;i++){
44                 buf[n-left] = tempBuf[i];
45                 left--;
46             }
47   
48             //If reach EOF.
49             if (left>0 && num<4) break;
50         }
51          
52         return n-left;
53         
54     }
55 }