HDU

题意：

给定一个集合，然后给定一个数，问集合中跟这个数异或值最大的数是啥

思路：

异或是位运算，可以看作二进制串来操作，想要异或值最大，，我们可以找到给定数的最优二进制串，然后对集合中数从高位到低位进行匹配，

用字典树存集合中的数，叶子结点附加值是这个数，

最后由给定的数匹配

#include<iostream> // studing#include<algorithm>#include<cstdio>#include<cstdlib>#include<cstring>#include<string>#include<cmath>#include<set>#include<queue>#include<stack>#include<map>#define PI acos(-1.0)#define in freopen("in.txt", "r", stdin)#define out freopen("out.txt", "w", stdout)using namespace std;typedef long long ll;typedef unsigned long long ull;const int maxn = 1e5 + 7, maxd = 20 + 7, mod = 1e9 + 7;const int INF = 0x7f7f7f7f;int T, ch[maxn*32][2], n, m, sz;ll a;void ins(ll x) {    int u = 0;    for(int i = 31; i >= 0; --i) {        int c = ( (x & (1L<<i)) ? 1 : 0 );        if(!ch[u][c]) { ch[sz][0] = ch[sz][1] = 0; ch[u][c] = sz++; }        u = ch[u][c];    }}ll find_(ll x) {    ll sum = 0;    int u = 0;    for(int i = 31; i >= 0; --i) {        int c = ( (x & (1L<<i)) ? 1 : 0 );        if(ch[u][!c]) { sum |= ( (!c) ? (1L<<i) : 0 ); u = ch[u][!c]; }        else { sum |= (c ? (1L << i) : 0); u = ch[u][c]; }    }    return sum;}int main() {    scanf("%d", &T);    for(int tt = 1; tt <= T; ++tt) {        scanf("%d %d", &n, &m);        ch[0][0] = ch[1][0] = 0;        sz = 1;        while(n--) { scanf("%lld", &a); ins(a); }        printf("Case #%d:\n", tt);        while(m--) { scanf("%lld", &a); printf("%lld\n", find_(a)); }    }    return 0;}