hdu5536 Chip Factory

Problem Description

John is a manager of a CPU chip factory, the factory produces lots of chips everyday. To manage large amounts of products, every processor has a serial number. More specifically, the factory produces  n chips today, the  i-th chip produced this day has a serial number  si.

At the end of the day, he packages all the chips produced this day, and send it to wholesalers. More specially, he writes a checksum number on the package, this checksum is defined as below:

maxi,j,k(si+sj)⊕sk

which  i,j,k are three  different integers between  1 and  n. And  ⊕ is symbol of bitwise XOR.

Can you help John calculate the checksum number of today?

 

Input

The first line of input contains an integer  T indicating the total number of test cases.

The first line of each test case is an integer  n, indicating the number of chips produced today. The next line has  n integers  s1,s2,..,sn, separated with single space, indicating serial number of each chip.

1≤T≤1000
3≤n≤1000
0≤si≤109
There are at most  10 testcases with  n>100

 

Output

For each test case, please output an integer indicating the checksum number in a line.

 

Sample Input

2 3 1 2 3 3 100 200 300

 

Sample Output

6 400

 

题意：给你n个数，让你找出3个不同下标对应的数，使得(s[i]+s[j])^s[k]的值最大。

思路：我们可以建一棵trie树，先把n个数都插入，然后枚举n*n个(i,j),先把trie树上的s[i],s[j]先消去，然后在树上找到异或和最大的k。我们每个节点记录一个val值。
插入时对所有经过节点的val值加1，删除就将对应节点的val值减1。在树上匹配的时候就只走那些val值为正的节点。匹配的过程中，首先看树中最高位能否异或得到1。
能的话就往能的那个方向走，否则往另外一个方向走。

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