LeetCode – Refresh – Read N Characters Given Read4 II

Since it need to record the previous chars, we just have to maintain a queue. Actually, the number of left chars are no larger than 4.

 

// Forward declaration of the read4 API.
int read4(char *buf);

class Solution {
private:
    queue<char> container;
public:
    /**
     * @param buf Destination buffer
     * @param n   Maximum number of characters to read
     * @return    The number of characters read
     */
    int read(char *buf, int n) {
        int len = 0, each = INT_MAX;
        while (!container.empty()) {
            *buf = container.front();
            container.pop();
            buf++;
            len++;
        }
        while (len < n && (each = read4(buf))) {
            len += each;
            buf += each;
        }
        if (len >= n) {
            for (int i = 0; i < len - n; i++) {
                container.push(buf[n-len+i]);
            }
            buf[n-len] = '\0';
            len = n;
        }
        return len;
    }
};