The XOR Largest Pair-dictionary tree Trie

From "Algorithm Competition Advanced Guide" 0x16

POJ / AcWing143

/*
数据为10^5，朴素方法O（N^2）会TLE
可以利用小于O（NlogN）方法，想到可以利用字典树加贪心优化
字典树插入，查询等基本模板如下
*/


#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;

const int N = 100010, M = 4000050;
int pos;
int son[M][2], a[N];

void insert(int x){
    
    
    int p = 0;
    for(int i = 30; ~i; i--){
    
    
        int &s = son[p][x >> i & 1];
        if(!s)s = ++pos;
        p = s;
    }
}

int query(int x){
    
    
    int p = 0, res = 0;
    for(int i = 30; ~i; i--){
    
    
        int s = x >> i & 1;
        if(son[p][!s]){
    
    
            res += 1 << i;
            p = son[p][!s];
        }else p = son[p][s];
    }
    return res;
}

int main(){
    
    
    int n, ans = 0;
    cin >> n;
    for(int i = 1; i <= n; i++){
    
    
        cin >> a[i];
        insert(a[i]);
    }
    for(int i = 1; i <= n; i++){
    
    
        ans = max(ans, query(a[i]));
    }
    cout << ans << endl;
    return 0;
}