LeetCode - 900. RLE iterator

class RLEIterator {
    
    private int[] encoding;
    private int tail;
    public RLEIterator(int[] encoding) {
    
       this.encoding = encoding;
       this.tail = 0;
    }
    
    public int next(int n) {
    
        int num = n;
        int len = encoding.length;
        while(tail < len && num > encoding[tail]){
    
            num -= encoding[tail];
            tail += 2;
        }
        if(tail < len){
    
            encoding[tail] -= num;
            return encoding[tail+1];
        }   
        else
           return -1;
    }
}