LeetCode-157-Read-N-Characters-Given-Read4.java

/*
Use read4() to implement read(), return the actual number read.
Becareful, it's possible that the actual number of elements in buf is < n

https://leetcode.com/discuss/85767/java-easy-version-to-understand

*/

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

public class Solution extends Reader4 {
    // 1.
    /**
     * @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) {
//         if(n <= 0) return 0;
        
//         char[] tmp = new char[4];
//         int j = 0;
        
//         while(true){
//             int readCount = read4(tmp); //put data from read4 into tmp
            
//             // copy date from temp to buf
//             for(int i = 0; i < readCount && j < n; j++, i++){
//                 buf[j] = tmp[i];
//             }
            
//             // readCount < 4 means file is all read. j==n means we have already get all we need from file.
//             if(readCount < 4 || j == n){
//                 break;
//             }
//         }
        
//         return j;
//     }
    
    // 2.
    /**
     * @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 total = 0;
        char[] buf4 = new char[4];
        while (total < n) {
            int count = read4(buf4);
            count = Math.min(count, n - total);
            
            int k = 0;
            while(total < n && k < count) buf[total++] = buf4[k++];
            
            if (count < 4) break;       // means we reached the EOF
        }
        
        return total;
    }
      
    // Another way
    public int read(char[] buf, int n) {
        int total = 0;
        
        char[] buf4 = new char[4];
        int len4 = read4(buf4);
        while (len4 > 0) {
            if (total >= n) break;
            len4 = Math.min(len4, n - total);
            
            int k = 0;
            while(total < n && k < len4) buf[total++] = buf4[k++];
            
            buf4 = new char[4];
            len4 = read4(buf4);
        }
        
        return total;
    }
}