HackerRank C++ Algorithms: Lonely Integer solution (Bit Manipulation)

HackerRank C++ solution for the Bit Manipulation Algorithms coding challenge called Lonely Integer. This C++ algorithm uses the sort function to sort an array in ascending order, and utilizes the bitwise XOR operator to compare integers and find the unique number in the array.

[PurnaChandraReddyTallapaka]

*WE CAN SOLVE THIS PROBLEM EASILY BY USING STACK*
*ALTHOUGH IT WONT WORK IF THERE ARE 2 UNIQUE ELEMENT BUT FOR THIS PROGRAMM THIS IS ENOUGH*

int lonelyinteger(vector<int> a) {

sort(a.begin(), a.end());
stack<int> res;
for(unsigned int i=0;i<a.size();i++)
{
if(res.empty())
res.push(a[i]);
else if (res.top()==a[i])
res.pop();
else
res.push(a[i]);
}
return res.top();
}

[john_paul]

This helped me a lot with reasoning through it myself on HackerRank! Something that can be improved is the complexity and legibility of your condition statement for the while loop. You use "i <= a.size() -1" when "i < a.size()" fulfills the same purpose and is easier to read. Moreover, performing bitwise comparison with the rare '^' operator is unnecessary in this case because simply checking for equality with an "==" works just as well. Nice ideas though; you helped me a lot in figuring it all out!

My solution: (C++)
int lonelyInteger(vector<int>& a) {
// Sort vector in increasing order (e.g., [5, 4, 9, 1, 9, 5, 4] becomes [1, 4, 4, 5, 5, 9, 9])
sort(a.begin(), a.end());
// Counter variable for while condition
int i = 0;
// Iterate through vector and compare each element to its successor
while(i < a.size() && a[i] == a[i+1])
{

// Matches come in pairs, so increment by 2 if a match is found
i+=2;
}
// Return mismatched value
return a[i];
}

[taynaracruz]

The complexity is actually O(nlogn) because you have to sort the array

[PIYUSH-lzzq]

can you tell me whats wrong in this code please ---

int lonelyinteger(vector<int> a) {
int n=a.size();
int arr[101];
for(int i=0;i<n;i++){
int ele=a[i];
arr[ele]++;
}
for(int i=0;i<101;i++){
if(arr[i]==1){
return arr[i];
}
}
}