The XOR Largest Pair -526互联

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<cstring>

using namespace std;

int bit[32];
int n, num[5211314];

struct Trie {
	int trie[5211314][2], tot = 1;
	inline void Insert(int a) {
		int p = 1;
		for (int i = 30; i >= 0; -- i){
			//num[i] < 2^31 所以只用开到 30
			bool flag = (bit[i] & a);
			if (trie[p][flag] == 0) {
				trie[p][flag] = ++ tot;
			}
			p = trie[p][flag];
		}
	}
	inline int Query() {
		int final = 0;
		for (int i = 1; i <= n; ++ i) {
			int now = 0, p = 1;
			//遍历每一个数找最大maxn
			//因为异或是相同为1不同为0
			//所以在同一位置贪心找不一样的数(若num[i]为0则找1，若num[i]为1则找0)
			for (int j = 30; j >= 0; -- j) {
				bool flag = !(bit[j] & num[i]);
				if (trie[p][flag] != 0) {
					//若有不同的
					p = trie[p][flag];
					now += flag;
				}
				else {
					//若没有不相同的
					p = trie[p][!flag];
					now += (!flag);
				}
				if (j != 0) now <<= 1;
			}
			final = max(final, (num[i] ^ now));
			//更新
		}
		return final;
	}
}tree;

int main() {
	bit[0] = 1;
	for (int i = 1; i <= 31; ++ i) {
		bit[i] = (bit[i - 1] << 1);
	}
	scanf("%d", &n);
	for (int i = 1; i <= n; ++ i) {
		scanf("%d", &num[i]);
		//记录每一个数
		tree.Insert(num[i]);
	}
	cout << tree.Query() << endl;
	return 0;
}