D. Xenia and Bit Operations

#include <bits/stdc++.h>

using namespace std;

int tree[2*(1<<17)];
int ar[1<<17];
int n, m, N;

int comb(int a, int b, int level){
    if((N - level) % 2 == 0)
        return a | b;
    return a ^ b;
}

int build(int i, int l, int r, int level){
    if(r == l)
        return tree[i] = ar[l];
    int mid = (l + r) / 2;
    return tree[i] = comb(build(2*i, l, mid, level+1), build(2*i+1, mid+1, r, level+1), level);
}

int query(int i, int l, int r, int p, int b, int level){
    if(r == l)
        return tree[i] = b;
    int mid = (l + r) / 2;
    if(p <= mid)
        return tree[i] = comb(query(2*i, l, mid, p, b, level+1), tree[2*i+1], level);
    else
        return tree[i] = comb(query(2*i+1, mid+1, r, p, b, level+1), tree[2*i], level);
}

int main(){

    scanf("%d%d", &n, &m);

    N = n;
    n = 1 << n;

    for(int i=0;i<n;i++){
        scanf("%d", &ar[i]);
    }

    build(1, 0, n-1, 1);

    /*for(int i=1;i<2*n;i++){
        printf("%d ", tree[i]);
    }*/

    for(int i=1;i<=m;i++){
        int p, b;
        scanf("%d%d", &p, &b);
        printf("%d\n", query(1, 0, n, p, b, 1));
    }

    return 0;
}