HDU5119 - Happy Matt Friends

做法：拆成两堆数，分别暴力出两组的所有异或值A,B，枚举A, 将B全部插入Trie树，通过枚举的数每一位的值,确定异或后构成的新树，然后在新树上统计比m大的值的个数即可。

#include <bits/stdc++.h>
#define pb push_back
typedef long long ll;
const int N = 1e6 + 7;
using namespace std;
int n, m, a[42], b[42], numa, numb;
ll ans = 0;
vector<int> va;
struct node{int ch[2], num;void init() {ch[0] = ch[1] = -1;num = 0;}
}T[N*20];
int cc, rt;
void ins(int x) {int now = rt;for(int i = 22; i >= 0; --i) {int t = !!(x&(1<<i));if(T[now].ch[t] == -1) {T[now].ch[t] = ++cc;T[cc].init();}++T[now].num;now = T[now].ch[t];}++T[now].num;
}
int cal(int x) {int now = rt, ff = 0, ans = 0;for(int i = 22; i >= 0; --i) {int t = !!(m&(1<<i));int f = !!(x&(1<<i));if(!t) {if(T[now].ch[1^f]!=-1) ans += T[T[now].ch[1^f]].num;now = T[now].ch[0^f];}else {now = T[now].ch[1^f];}if(now == -1) break;}if(now != -1) ans+=T[now].num;return ans;
}
int TT, CC = 0;
int main() {memset(T,0,sizeof(T));scanf("%d",&TT);while(TT--) {scanf("%d%d",&n,&m);for(int i = 0; i < n; ++i) scanf("%d",&a[i]);numa = n/2; numb = 0;for(int i = numa; i < n; ++i) b[numb++] = a[i];ans = 0;va.clear();for(int s = 0; s < (1<<numa); ++s) {int tmp = 0;for(int i = 0; i < numa; ++i) if(s&(1<<i)) tmp^=a[i];va.pb(tmp);}rt = cc = 0;rt = ++cc;T[rt].init();for(int s = 0; s < (1<<numb); ++s) {int tmp = 0;for(int i = 0; i < numb; ++i) if(s&(1<<i)) tmp^=b[i];ins(tmp);}for(int i = 0; i < va.size(); ++i) ans += 1LL*cal(va[i]);printf("Case #%d: %lld\n",++CC,ans);for(int i = 1; i <= cc; ++i) T[i].init();}
}