hdu4825 01字典树+贪心

从高位向低位构造字典树，因为高位得到的数更大。

AC代码：

#include<cstdio>
using namespace std;
typedef long long LL;
const int maxn=2;
struct node{
	node *next[maxn];
	node(){
		next[0]=next[1]=NULL;
	}
}*root;

LL w[50];
void deal(){
	w[0]=1;
	for(int i=1;i<=36;++i) w[i]=w[i-1]*2;
}
void Init(){
	root = new node();
}
void insert_tree(LL num){
	node *p=root,*q;
	for(int i=32;i>=0;--i){
		LL h=num&w[i];
		int u=0;
		if(h!=0) u=1;
		if(p->next[u]==NULL){
			q=new node();
			p->next[u]=q;
			p=p->next[u];
		}
		else {
			p=p->next[u];
		}
	}
}
LL getAns(LL num,node *u,int lev){
	if(lev<0||u==NULL) return 0;
	LL ans=0;
	int h=num&w[lev];
	if(h!=0) h=1;
	h=1-h; //xor
	if(u->next[h]==NULL) ans+=(1-h)*w[lev]+getAns(num,u->next[1-h],lev-1);
	else ans+=h*w[lev]+getAns(num,u->next[h],lev+-1);
	return ans;
}
void free_tree(node *u){ //释放内存
	if(u==NULL) return;
	free_tree(u->next[0]);
	free_tree(u->next[1]);
	delete u;
}
int main(){
	deal();
	int T,n,m,kase=1;
	LL x;
	scanf("%d",&T);
	while(T--){
		Init();
		scanf("%d%d",&n,&m);
		for(int i=0;i<n;++i) {
			scanf("%lld",&x);
			insert_tree(x);
		}
		printf("Case #%d:\n",kase++);
		LL S;
		for(int i=0;i<m;++i){
			scanf("%lld",&S);
			printf("%lld\n",getAns(S,root,32));
		}
		free_tree(root);
	}
	return 0;
}

如有不当之处欢迎指出！