My code is giving wrong answer. Can anyone explain why?

help
1

Here is the question link
This the code which gives me correct output but in submission it shows me wrong answer. Please help me out & explain why it’s happening?

#include <bits/stdc++.h>
using namespace std;
int main() {
	int t;
	cin>>t;
	while(t--){
	    int n,i;
        cin>>n;
	    int arr[n];
	    bool flag = false;
	    for (int i = 0; i < n; i++) {
	        cin>>arr[i];
	    }
	    sort(arr, arr+n);
	    for (i = 0; i < n; i=i+2){
	        if(arr[i]==arr[i+1]){
                flag = true;
	        }
	        else{
	            flag = false;
	        }
	    }
	    if(flag == false){
	    cout<<arr[n-1];
	    }
	}
	return 0;
}
2

Index-out-of-bounds access for sample test input:

[simon@simon-laptop][11:40:06]
[~/devel/hackerrank/otherpeoples]>./compile-latest-cpp.sh 
Compiling arnab2002-MISSP.cpp
Executing command:
  g++ -std=c++17 arnab2002-MISSP.cpp -O3 -g3 -Wall -Wextra -Wconversion -DONLINE_JUDGE -D_GLIBCXX_DEBUG    -fsanitize=undefined -ftrapv
Successful
[simon@simon-laptop][11:40:14]
[~/devel/hackerrank/otherpeoples]>echo "1
5
1
1
2
2
3" | ./a.out
arnab2002-MISSP.cpp:16:28: runtime error: index 5 out of bounds for type 'int [*]'
3

Edit:

Once you’ve fixed that, consider the test input:

2
3
1 
2
1
3
1 
2
1

Edit:

Then after you’ve fixed that, consider the test input:

1                
5
1
1
2
3
3
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