lc​​448. 找到所有数组中消失的数字​

​​448. 找到所有数组中消失的数字​​

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给你一个含 ​​n​​ 个整数的数组 ​​nums​​ ，其中 ​​nums[i]​​ 在区间 ​​[1, n]​​ 内。请你找出所有在 ​​[1, n]​​ 范围内但没有出现在 ​​nums​​ 中的数字，并以数组的形式返回结果。

示例 1：

输入：nums = [4,3,2,7,8,2,3,1]
输出：[5,6]

示例 2：

输入：nums = [1,1]
输出：[2]

提示：

• ​​n == nums.length​​
• ​​1 <= n <= 105​​
• ​​1 <= nums[i] <= n​​

进阶：你能在不使用额外空间且时间复杂度为 ​​O(n)​​ 的情况下解决这个问题吗? 你可以假定返回的数组不算在额外空间内。

class Solution {
    public List<Integer> findDisappearedNumbers(int[] nums) {
// Hash table for keeping track of the numbers in the array
        // Note that we can also use a set here since we are not
        // really concerned with the frequency of numbers.
        HashMap<Integer, Boolean> hashTable = new HashMap<Integer, Boolean>();

        // Add each of the numbers to the hash table
        for (int i = 0; i < nums.length; i++) {
            hashTable.put(nums[i], true);
        }

        // Response array that would contain the missing numbers
        List<Integer> result = new LinkedList<Integer>();

        // Iterate over the numbers from 1 to N and add all those
        // that don't appear in the hash table.
        for (int i = 1; i <= nums.length; i++) {
            if (!hashTable.containsKey(i)) {
                result.add(i);
            }
        }

        return result;
    }
}