Maximum xor Value Pair n an Array Without Using Tries

I am not understanding the implementation of the question in Blog(M) complexity can anyone please help me to understand the flow of the problem.
this is the implementaiton:
#include<bits/stdc++.h> using namespace std; // Utility function to check number of elements // having set msb as of pattern int checkBit(int pattern, int arr[], int n) { int count = 0; for (int i = 0; i < n; i++) if ((pattern & arr[i]) == pattern) count++; return count; } // Function for finding maximum and value pair int maxAND (int arr[], int n) { int res = 0, count; // iterate over total of 30bits from msb to lsb for (int bit = 31; bit >= 0; bit) { // find the count of element having set msb count = checkBit(res  (1 << bit),arr,n); // if count >= 2 set particular bit in result if ( count >= 2 ) res = (1 << bit); } return res; } // Driver function int main() { int arr[] = {4, 8, 6, 2}; int n = sizeof(arr)/sizeof(arr[0]); cout << "Maximum AND Value = " << maxAND(arr,n); return 0; }