static int findMissingNumber(int start, int end, List<Integer> list) {    Number numdel = 0;    Number delsum = 0;    int num = 0;    for (int i = start; i <= end; i++) {        num = num + i;    }    for (Number n : list) {        numdel = (Integer)numdel + (Integer)n;        delsum = (Integer)num - (Integer)numdel;    }    return (int) delsum;}

感觉有点笨但是没啥大问题，要是多删几个数不行了