Create Read N Characters Given Read4 II - Call multiple times.js

Author: paopao2

Read N Characters Given Read4 II - Call multiple times.js

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+/**
+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. 
+*/
+/**
+ * Definition for read4()
+ * 
+ * @param {character[]} buf Destination buffer
+ * @return {number} The number of characters read
+ * read4 = function(buf) {
+ *     ...
+ * };
+ */
+
+/**
+ * @param {function} read4()
+ * @return {function}
+ */
+var solution = function(read4) {
+    let helperBuf = [];
+    let count = 0; // how many characters read with read4
+    let i = 0;
+        
+    /**
+     * @param {character[]} buf Destination buffer
+     * @param {number} n Maximum number of characters to read
+     * @return {number} The number of characters read
+     */
+    return function(buf, n) {
+        let pointer = 0;
+        
+        while (pointer < n) {
+            if (i === 0) {
+                count = read4(helperBuf);
+            }
+            
+            while (i < count && pointer < n) {
+                buf[pointer++] = helperBuf[i++];
+            }
+            
+            // read4 buffer used up, start over
+            if (i === count) {
+                i = 0;
+            }
+            
+            // end of file
+            if (count < 4) {
+                break;
+            }
+        }
+        
+        return pointer;
+    };
+};