暴力解法

class Solution {
    public List<Integer> findDisappearedNumbers(int[] nums) {
        List<Integer> list = new ArrayList<>();
        int n = nums.length;
        boolean[] b = new boolean[n + 1];
        for(int i : nums){
            b[i] = true;
        }
        for(int i = 1;i <= n;i++){
            if(!b[i]) list.add(i);
        }
        return list;
    }
}