FORCE-T0339D: Xenia and Bit Operations

#include <bits/stdc++.h>
using namespace std;

const int logN = 17;

int sm[1 << (logN + 1)];

int main(){

    int ex, Q;
    scanf("%d%d", &ex, &Q);
    for(int i = (1 << ex); i < (1 << (ex + 1)); ++i){
        scanf("%d", &sm[i]);
    }
    bool doOr = true;
    for(int e = ex - 1; e >= 0; --e){
        for(int i = (1 << e); i < (1 << (e + 1)); ++i){
            if(doOr){
                sm[i] = sm[i << 1] | sm[(i << 1) | 1];
            } else {
                sm[i] = sm[i << 1] ^ sm[(i << 1) | 1];
            }
        }
        doOr = !doOr;
    }
    while(Q--){
        int idx, x;
        scanf("%d%d", &idx, &x);
        idx += (1 << ex) - 1;
        sm[idx] = x;
        doOr = true;
        for(int i = idx >> 1; i >= 1; i >>= 1){
            if(doOr){
                sm[i] = sm[i << 1] | sm[(i << 1) | 1];
            } else {
                sm[i] = sm[i << 1] ^ sm[(i << 1) | 1];
            }
            doOr = !doOr;
        }
        cout << sm[1] << '\n';
    }

    return 0;
}