XOR Queries of a Subarray

Given the array arr of positive integers and the array queries where queries[i] = [Li, Ri], for each query i compute the XOR of elements from Li to Ri (that is, arr[Li] xor arr[Li+1] xor ... xor arr[Ri] ). Return an array containing the result for the given queries.

Example:

Input: arr = [1,3,4,8], queries = [[0,1],[1,2],[0,3],[3,3]]
Output: [2,7,14,8]
Explanation:

The binary representation of the elements in the array are:
1 = 0001 
3 = 0011 
4 = 0100 
8 = 1000 
The XOR values for queries are:
[0,1] = 1 xor 3 = 2 
[1,2] = 3 xor 4 = 7 
[0,3] = 1 xor 3 xor 4 xor 8 = 14 
[3,3] = 8

Example 2:

Input: arr = [4,8,2,10], queries = [[2,3],[1,3],[0,0],[0,3]]
Output: [8,0,4,4]

Constraints:

1 <= arr.length <= 3 * 10^4
1 <= arr[i] <= 10^9
1 <= queries.length <= 3 * 10^4
queries[i].length == 2
0 <= queries[i][0] <= queries[i][1] < arr.length

C++

class Solution {
public:
    // Utility function for preprocessing array XORs
    vector<int> preprocess(vector<int> arr) {
        // preprocess[i] = arr[0]^arr[1]^arr[2]...^arr[i]
        for(int i=1; i<arr.size(); i++)
            arr[i] ^= arr[i-1];
        
        return arr;
    }
    
    vector<int> xorQueries(vector<int>& arr, vector<vector<int>>& queries) {
        // Number of elements in the array
        int n = arr.size();
        
        // Preprocess XORs of all array elements
        vector<int> prefix = preprocess(arr);
        vector<int> answers;
        
        int left, right;
        for(auto query: queries) {
            int left = query[0];
            int right = query[1];
            
            // prefix[right] = arr[0]^arr[1]...^arr[right]
            if(left == 0)
                answers.push_back(prefix[right]);
            else
                // we use a property of XOR: A^B^A = B to remove
                // computed XORs that are not in the range
                answers.push_back(prefix[right]^prefix[left-1]);
        }
        
        return answers;
    }
};

@soham-parekh

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