CodeCraft-19 and Codeforces Round #537 (Div. 2) C. Creative Snap(二分+分治)

#include <bits/stdc++.h>
#define ll long long
#define maxn 100005
using namespace std;
int n, m, a, b;
int pre[maxn];

ll dfs(int l,int r){
  int xx = upper_bound(pre, pre + m, r) - lower_bound(pre, pre + m, l);
  if(xx == 0) return a;
  ll ans = (r - l + 1LL) * xx * b;
  int mid = (l + r) >> 1;
  if(l != r)
  ans = min(ans, dfs(l, mid) + dfs(mid + 1, r));
  return ans;
}

int main()
{
  scanf("%d%d%d%d",&n,&m,&a,&b);
  for(int i=0;i<m;i++){
    scanf("%d", &pre[i]);
  }
  sort(pre, pre + m);
  ll ans = dfs(1, 1 << n);
  printf("%lld\n", ans);
  return 0;
}