HDU 5536 Chip Factory 01trie

题目：

http://acm.hdu.edu.cn/showproblem.php?pid=5536

题意：

给出n个数，从这些数字中任选3个不同的数字x,y,z，求出一个值(x+y)⨁z，求所有值里面的最大值

思路：

暴力居然可过。。。然后正解是用字典树去求最大异或值，首先把n个数字插入到01trie中，然后枚举x+y，首先从字典树中删掉x,y，然后去查询与x+y异或能得出的最大值，最后取这些值中的最大值

#include <bits/stdc++.h>using namespace std;const int N = 1000 + 10, M = 2, INF = 0x3f3f3f3f;struct node{    node *next[M];    int val;    void init()    {        memset(next, 0, sizeof next);        val = 0;    }}trie[N*32], *root;int tot;int len = 31;node *new_node(){    trie[tot].init();    return trie + tot++;}void trie_init(){    tot = 0;    root = new_node();}void trie_insert(int x){    node *p = root;    for(int i = len-1; i >= 0; i--)    {        int j = 1 & (x>>i);        if(p->next[j] == NULL) p->next[j] = new_node();        p->next[j]->val++;        p = p->next[j];    }}int trie_query(int x){    node *p = root;    int ans = 0;    for(int i = len-1; i >= 0; i--)    {        int j = ! (1 & (x>>i));        if(p->next[j] != NULL && p->next[j]->val != 0)        {            p = p->next[j];            ans = ans * 2 + 1;        }        else        {            p = p->next[!j];            ans = ans * 2 + 0;        }    }    return ans;}void trie_del(int x){    node *p = root;    for(int i = len-1; i >= 0; i--)    {        int j = 1 & (x>>i);        p->next[j]->val--;        p = p->next[j];    }}int main(){    int t, n;    int a[N];    scanf("%d", &t);    while(t--)    {        trie_init();        scanf("%d", &n);        for(int i = 1; i <= n; i++)        {            scanf("%d", &a[i]);            trie_insert(a[i]);        }        int ans = 0;        for(int i = 1; i <= n; i++)            for(int j = i+1; j <= n; j++)            {                trie_del(a[i]); trie_del(a[j]);                ans = max(ans, trie_query(a[i] + a[j]));                trie_insert(a[i]); trie_insert(a[j]);            }        printf("%d\n", ans);    }    return 0;}

暴力代码：

#include <bits/stdc++.h>using namespace std;const int N = 1000 + 10, INF = 0x3f3f3f3f;int a[N];int main(){    int t, n;    scanf("%d", &t);    while(t--)    {        scanf("%d", &n);        for(int i = 1; i <= n; i++) scanf("%d", &a[i]);        int ans = 0;        for(int i = 1; i <= n; i++)            for(int j = i+1; j <= n; j++)                for(int k = j+1; k <= n; k++)                {                    ans = max(ans, (a[i] + a[j]) ^ a[k]);                    ans = max(ans, (a[j] + a[k]) ^ a[i]);                    ans = max(ans, (a[i] + a[k]) ^ a[j]);                }        printf("%d\n", ans);    }    return 0;}