# 448.find-all-numbers-disappeared-in-an-array

## Statement

``````输入：nums = [4,3,2,7,8,2,3,1]

``````

``````输入：nums = [1,1]

``````

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

Given an array `nums` of `n` integers where `nums[i]` is in the range `[1, n]`, return an array of all the integers in the range `[1, n]` that do not appear in `nums`.

Example 1:

``````Input: nums = [4,3,2,7,8,2,3,1]
Output: [5,6]
``````

Example 2:

``````Input: nums = [1,1]
Output: [2]
``````

Constraints:

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

Follow up: Could you do it without extra space and in `O(n)` runtime? You may assume the returned list does not count as extra space.

## Solution

``````#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define endl "\n"
#define fi first
#define se second
#define all(x) begin(x), end(x)
#define rall rbegin(a), rend(a)
#define bitcnt(x) (__builtin_popcountll(x))
#define complete_unique(a) a.erase(unique(begin(a), end(a)), end(a))
#define mst(x, a) memset(x, a, sizeof(x))
#define MP make_pair

using ll = long long;
using ull = unsigned long long;
using db = double;
using ld = long double;
using VLL = std::vector<ll>;
using VI = std::vector<int>;
using PII = std::pair<int, int>;
using PLL = std::pair<ll, ll>;

using namespace __gnu_pbds;
using namespace std;
template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const ll mod = 1e9 + 7;

template <typename T, typename S>
inline bool chmax(T &a, const S &b) {
return a < b ? a = b, 1 : 0;
}

template <typename T, typename S>
inline bool chmin(T &a, const S &b) {
return a > b ? a = b, 1 : 0;
}

#ifdef LOCAL
#include <debug.hpp>
#else
#define dbg(...)
#endif

class Solution {
public:
vector<int> findDisappearedNumbers(vector<int> &nums) {
int n = nums.size();
for (int i = 0; i < n; i++) {
int x = abs(nums[i]);
if (nums[x - 1] > 0) {
nums[x - 1] *= -1;
}
}

auto res = vector<int>();
for (int i = 0; i < n; i++) {
if (nums[i] > 0) {
res.push_back(i + 1);
}
}

return res;
}
};

#ifdef LOCAL

int main() {
return 0;
}

#endif
``````