新人求助

#include <bits/stdc++.h>
#define maxn 500010
#define ll long long
using namespace std;

struct data {
  int id, k;
  ll val;
  data(int _id = 0, int _k = 0, ll _val = 0) {
    id = _id, k = _k, val = _val;
  }
  bool operator < (const data &rhs) const {
    return val < rhs.val;
  }
};
struct node {
  int l, r, s;
} t[maxn * 40];
int rt[maxn], n, k, cnt = 0;
ll a[maxn], ans = 0;
priority_queue<data> pq;
template <class T> void read(T &x) {
  char ch = x = 0;
  bool fl = false;
  while (!isdigit(ch))
    fl |= ch == '-', ch = getchar();
  while (isdigit(ch))
    x = x * 10 + ch - '0', ch = getchar();
  x = fl ? -x : x;
}
void insert(int &x, int y, ll val, int d) {
  t[x = ++cnt] = t[y], t[x].s++;
  if (!~d)
    return;
  if (~val >> d & 1)
    insert(t[x].l, t[y].l, val, d - 1);
  else
    insert(t[x].r, t[y].r, val, d - 1);
}
ll query(int x, ll val, int k, ll tmp, int d) {
  if (!~d)
    return val ^ tmp;
  if (t[x].s < k)
    return -1;
  if (~val >> d & 1) {
    if (t[t[x].r].s >= k)
      query(t[x].r, val, k, tmp ^ (1LL << d), d - 1);
    else
      query(t[x].l, val, k - t[t[x].r].s, tmp, d - 1);
  } else {
    if (t[t[x].l].s >= k)
      query(t[x].l, val, k, tmp, d - 1);
    else
      query(t[x].r, val, k - t[t[x].l].s, tmp ^ (1LL << d), d - 1);
  }
}
int main() {
  read(n), read(k);
  for (int i = 1; i <= n; i++) {
    read(a[i]), a[i] ^= a[i - 1];
  }
  insert(rt[0], 0, 0, 32);
  for (int i = 1; i <= n; i++) {
    insert(rt[i], rt[i - 1], a[i], 32);
  }
  for (int i = 1; i <= n; i++) {
    ll res = query(rt[i - 1], a[i], 1, 0, 32);
    pq.push(data(i, 1, res));
  }
  while (k--) {
    data tmp = pq.top();
    ans += tmp.val, pq.pop();
    ll res = query(rt[tmp.id - 1], a[tmp.id], tmp.k + 1, 0, 32);
    if (~res)
      pq.push(data(tmp.id, tmp.k + 1, res));
  }
  printf("%lld\n", ans);
  return 0;
}