Added read n given read 4

Author: FreeTymeKiyan

Other/ReadNGivenRead4.java

@@ -0,0 +1,41 @@
+/**
+ * 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 will only be called once for each test case.
+ * 
+ * Tags: 
+ */
+class ReadNGivenRead4 {
+    
+    public static void main(String[] args) {
+        
+    }
+    
+    /**
+     * Call only 1 time
+     * Can reach n or end of file
+     * if read4 returns size smaller than 4, it means end of file
+     * the # of bytes read is the minimum of n - readBytes and size of read4
+     * Copy things in read4 buffer to output buffer
+     * Update readBytes
+     */
+    public int read(char[] buf, int n) {
+        char[] buffer = new char[4];
+        int readBytes = 0;
+        boolean eof = false; // flag
+        
+        while (!eof && readBytes < n) {
+            int size = read4(buffer); // read4 is given
+            if (size < 4) eof = true; // file end
+            int bytes = Math.min(n - readBytes, size); // reach n or end of file
+            // src, src pos, dest, dest pos, length
+            System.arraycopy(buffer, 0, buf, readBytes, bytes); // copy to 
+            readBytes += bytes;
+        }
+        return readBytes; // can be n or smaller
+    }
+}