LeetCode/problems/rle-iterator.java

class RLEIterator {
    private int[] encoding;
    private int major = 0;
    private int minor = 0;

    public RLEIterator(int[] encoding) {
        this.encoding = encoding;
    }

    private void nextSegment() {
        major += 2;
        minor = 0;
    }

    private int lastConsumed() {
        if (major == 0 && minor == 0) {
            // Haven't consumed anything
            return -1;
        } else if (major <= encoding.length && minor == 0) {
            // Consumed last element of a previous segment
            return encoding[major - 1];
        } else if (major >= encoding.length) {
            // Everything was consumed
            return -1;
        }

        // Last consumed from the current segment
        return encoding[major + 1];
    }

    public int next(int n) {
        while (n > 0 && major < encoding.length) {
            int consumed = Math.min(n, encoding[major] - minor);

            n -= consumed;
            minor += consumed;

            if (minor == encoding[major]) {
                nextSegment();
            }
        }

        if (n > 0) {
            return -1;
        }

        return lastConsumed();
    }
}

/**
 * Your RLEIterator object will be instantiated and called as such:
 * RLEIterator obj = new RLEIterator(encoding);
 * int param_1 = obj.next(n);
 */