【CF888G】Xor-MST

题面

https://www.luogu.org/problem/CF888G

题解

#include<cstdio>
#include<iostream>
#include<cstring>
#include<vector>
#define ri register int
#define N 200050
#define LL long long 
#define INF (1<<30)
using namespace std;
int n;
int a[N];
LL ans=0;

inline int dit(int x,int i){
  if (x&(1<<i)) return 1; else return 0;
}

struct TRIE {
  int ch[N*30][2],tot;
  void init() {tot=0;}
  void clear() {
    for (ri i=0;i<=tot;i++) ch[i][0]=ch[i][1]=0;
  tot=0;
  }
  void insert(int x) {
    int now=0;
  for (ri i=30;i>=0;i--) {
    int d=dit(x,i);
    if (!ch[now][d]) ch[now][d]=++tot;
    now=ch[now][d];
  }
  }
  int search(int x) {
  int ret=0,now=0;
  for (ri i=30;i>=0;i--) {
    int d=dit(x,i);
    if (ch[now][d]) now=ch[now][d]; else now=ch[now][d^1],ret+=(1<<i);
  }
  return ret;
  }
} trie;

void solve(vector<int> s,int d){
  int l=s.size();
  if (l==0 || l==1) return;
  if (d==-1) return;
  vector<int> s1,s2; s1.clear(); s2.clear();
  for (ri i=0;i<l;i++) if (s[i]&(1<<d)) s1.push_back(s[i]); else s2.push_back(s[i]);
  int l1=s1.size(),l2=s2.size();
  if (l1 && l2) {
    trie.clear();
  int ret=INF;
  for (ri i=0;i<l1;i++) trie.insert(s1[i]);
  for (ri i=0;i<l2;i++) ret=min(ret,trie.search(s2[i]));
  ans+=ret;
  solve(s1,d-1); solve(s2,d-1);
  }
  else if (l1) solve(s1,d-1); else solve(s2,d-1);
}

int main(){
  scanf("%d",&n);
  for (ri i=1;i<=n;i++) scanf("%d",&a[i]);
  vector<int> s; s.clear();
  for (ri i=1;i<=n;i++) s.push_back(a[i]);
  trie.init();
  solve(s,30);
  cout<<ans<<endl;
  return 0;
}