求两个数异或最大值

题目链接：http://acm.hust.edu.cn/vjudge/contest/view.action?cid=98837#problem/I

题意：给定一些数，求这些数中异或值最大的值

分析：每个数都可以写成二进制，可以建立一颗字典树

#include<bits/stdc++.h>

using namespace std;

#define INF 0x3f3f3f3f

const int N = 100000<<5;  
  
struct Trie {  
    int a[2];  
    int num;  
} f[N];  
  
int cnt, ans;  
  
// insert x into the root which id is u, the deep is num  
void insert(int x, int u, int num) 
{  
    bool k;  
    for (int i = num; i >= 0; i--) 
    {  
        k = (1<<i)&x;  
        if (f[u].a[k] == -1)  
            f[u].a[k] = ++cnt;  
        u = f[u].a[k];  
    }  
    f[u].num = x;  
}  
  
// query xor  
void query(int x, int u, int num) 
{  
    bool k;  
    for (int i = num; i >= 0; i--) 
    {  
        k = (1<<i)&x;  
        if (f[u].a[!k] != -1)  
            u = f[u].a[!k];  
        else  
            u = f[u].a[k];  
    }  
    ans = max(ans, f[u].num^x);  
}  
  
int main() 
{  
    int n, t;  
    while(scanf("%d", &n)!=EOF) 
    {  
        memset(f, -1, sizeof(Trie) * N);  
        cnt = 0;  
        ans = 0;  
        while (n--) 
        {  
            scanf("%d", &t);  
            insert(t, 0, 31);  
            query(t, 0, 31);  
        }  
        printf("%d
", ans);  
    }  
    return 0;  
}