158 Read N Characters Give Read4 II - Call Multiple Times.js

// 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.

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// Hide Similar Problems (E) Read N Characters Given Read4



/**
 * 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 bufRead = [];
    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 numChrRead = 0;
        
        while (numChrRead < n) {
            if (i === 0) {
                count = read4(bufRead);
            }
            
            while (i < count && numChrRead < n) {
                buf[numChrRead++] = bufRead[i++];
            }
            
            // read4 buffer used up, start over
            if (i === count) {
                i = 0;
            }
            
            // end of file
            if (count < 4) {
                break;
            }
        }
        
        return numChrRead;
    };
};