HDU 4825 Xor Sum（01字典树）题解

思路：先把所有数字存进字典树，然后从最高位贪心。

代码：

#include<set>
#include<map>
#include<stack>
#include<cmath>
#include<queue>
#include<vector>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
typedef long long ll;
const int maxn = 100000 + 10;
const int seed = 131;
const ll MOD = 1e9 + 7;
const ll INF = 1e17;
using namespace std;
int ch[32 * maxn][2], tot;
ll val[32 * maxn];
void init(){
    tot = 1;
    memset(ch[0], 0, sizeof(ch[0]));
}
void Insert(ll x){
    int root = 0;
    for(int i = 31; i >= 0; i--){
        int u = (x >> i) & 1;
        if(ch[root][u] == 0){
            memset(ch[tot], 0, sizeof(ch[root]));
            ch[root][u] = tot++;
        }
        root = ch[root][u];
    }
    val[root] = x;
}
ll query(ll x){
    int root = 0;
    for(int i = 31; i >= 0; i--){
        int u = (x >> i) & 1;
        if(ch[root][!u] != 0){
            root = ch[root][!u];
        }
        else root = ch[root][u];
    }
    return val[root];
}
int main(){
    int T, Case = 1;
    scanf("%d", &T);
    while(T--){
        init();
        int n, m;
        scanf("%d%d", &n, &m);
        for(int i = 0; i < n; i++){
            ll x;
            scanf("%lld", &x);
            Insert(x);
        }

        printf("Case #%d:\n", Case++);
        while(m--){
            ll x;
            scanf("%lld", &x);
            printf("%lld\n", query(x));
        }
    }
    return 0;
}