> For the complete documentation index, see [llms.txt](https://gl01.gitbook.io/gfg-editorials/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gl01.gitbook.io/gfg-editorials/2024/06-2024-june-1/02-construct-list-using-given-q-xor-queries.md).

# 02. Construct list using given q XOR queries

The problem can be found at the following link: [Question Link](https://www.geeksforgeeks.org/problems/construct-list-using-given-q-xor-queries/1)

## My Approach

* Initialize an empty vector `ans` and add `0` to it. Also, initialize a variable `xorr` to `0`.
* Iterate through each query in `queries`.
  * If the first element of the query `x[0]` is `1`, update `xorr` by XORing it with `x[1]`.
  * If the first element of the query `x[0]` is `0`, append `xorr XOR x[1]` to `ans`.
* After processing all queries, XOR each element in `ans` with the final value of `xorr`.
* Sort the `ans` vector.
* Return the sorted `ans` vector.

## Time and Auxiliary Space Complexity

* **Time Complexity**: `O(n log n)`, where n is the number of elements in `ans` due to the sorting step. Each query operation (XOR and append) takes constant time.
* **Auxiliary Space Complexity**: `O(n)`, where n is the number of elements in the `ans` vector.

## Code (C++)

```cpp
class Solution {
public:
    vector<int> constructList(int q, vector<vector<int>> &queries) {
        vector<int>ans;
        ans.push_back(0);
        int xorr=0;
        for(auto x:queries){
            if(x[0]) xorr^=x[1];
            else ans.push_back(xorr^x[1]);
        }
        for(int &x:ans) x^=xorr;
        sort(begin(ans), end(ans));
        return ans;
    }
};
```

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