zxa had a great interest in exclusive disjunction(i.e. XOR) recently, therefore he took out a non-negative integer sequence a1,a2,⋯,an of length n.
zxa thought only doing this was too boring, hence a function funct(x,y) defined by him, in which ax would be changed into y irrevocably and then comput

分析：兩次異或同一個數返回原數。先全算一次，在修改！
#include<iostream>
#include<cstring>
#include<string>
#include<algorithm>
#include<cmath>
using namespace std;
int a[100000];
int main()
{
    int t;
    cin>>t;
    while(t--)
    {
        int n,m,ans=0;
        cin>>n>>m;
        for
 
(int i=1;i<=n;i++)
        {
            cin>>a[i];
        }

        for(int i=1;i<n;i++)
        {
            for(int j=i+1;j<=n;j++)
            {
                ans^=(a[i]+a[j]);
            }
        }
        for(int i=0;i<m;i++)
        {
            int r,l;
            cin
 
>>r>>l;
            for(int k=1;k<=n;k++)
            {
                if(k!=r)
                ans^=(a[k]+a[r]),ans^=(a[k]+l);
            }
            a[r]=l;
            cout<<ans<<endl; 
        }
    }
    return 0;
}