I was tryping to solve problem https://mirror.codeforces.com/problemset/problem/617/E. I am using Mo's algorithm to solve this problem, but this giving me wrong ans on test case 7. Please help to find where did my code fail.

My Code

include <bits/stdc++.h>

using namespace std;

// shortcuts

define M 1000000007

define ll long long

define lld long double

define vi vector

define vll vector

define mx 1e18

define mn INT_MIN

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ static bool cmp(vector &a , vector &b) { if(a[0]/319 != b[0]/319) return a[0]/319 < b[0]/319; else return a[1] < b[1]; }

void ok(ll t) { ll n , q , k; cin >> n >> q >> k; vector vt(n+1) , prefix(n+1 , 0); for(ll i = 1; i <= n; i++) cin >> vt[i]; for(ll i = 1; i <= n; i++) prefix[i] = prefix[i-1]^vt[i];

ll mp[1000500] = {0};
vector<vector<ll>> query(q , vector<ll>(3));
for(ll i = 0; i < q; i++) 
{
    cin >> query[i][0] >> query[i][1];
    query[i][0]-=1;
    query[i][2] =i;
}
sort(query.begin(), query.end() , cmp);

ll total = 0;
vector<ll> ans(q , 0);
ll left = 0 , right = -1;
for(ll i = 0;i<q;i++)
{
    // cout << query[i][0] << " " << query[i][1] << " " << query[i][2] << endl;
    while(left > query[i][0]) // add
    {
        left-=1;
        total += mp[k^prefix[left]];
        mp[prefix[left]]+=1;
    }
    while(right < query[i][1]) // add
    {
        right+=1;
        total += mp[k^prefix[right]];
        mp[prefix[right]]+=1;
    }
    while(left < query[i][0]) // remove
    {
        mp[prefix[left]]-=1;
        total -= mp[k^prefix[left]];
        left+=1;
    }
    while(right > query[i][1]) // remove
    {
        mp[prefix[right]]-=1;
        total -= mp[k^prefix[right]];
        right-=1;
    }
    ans[query[i][2]] = total;
}

for(ll i = 0;i<q;i++) cout << ans[i] << endl;

}

int main() { // Shubham Kumar Jha ios_base::sync_with_stdio(false); cin.tie(NULL);

ifndef ONLINE_JUDGE

freopen("zinput.txt", "r", stdin);
freopen("zoutput.txt", "w", stdout);

endif

ll t = 1;
// cin >> t;
for(ll i = 1;i<=t;i++)
{
    ok(i);
}
return 0;

}