求数组中最大的异或值 20171013

Suppose you have an integer sequence, we define a lucky number as a special integer which is the XOR value of the sequence’s greatest and strict second greatest element. For example, in [1,2,3,3], 3 is the greatest element and 2 is the strict second greatest one, even though we have two 3 at the same time; so the lucky number is 2 xor 3 = 1.
Now given an N-length integer sequence, please find out the maximum lucky number of all continuous subsequences.

输入描述：
The first line is an integer n, representing the length of the value of V[i](1 <= V[i] <= 10^8) in the sequence respectively. We’ll ensure that there are at least two different values from V[1] to V[n. Define the continuous subsequence as [V[1],V[l+1],V[l+2], … ,V[r]] ( 1 <= l <= r <= n)
30% small input: 2 <= n <= 10
40% medium input: 2 <= n <= 5000
30% large input: 2 <= n <= 100000

输出描述：
Output the greatest lucky number

示例1：

输入
5
5 2 1 4 3

输出
7

python代码

array_length = raw_input()array = raw_input()num = [int(n) for n in array.split()]q = []ans = -999for value in num:    while q and q[-1] <= value:#最大的情况        ans = max(ans,q[-1]^value)        q.pop()    if q:#次大的情况        ans = max(ans,q[-1]^value)    q.append(value)print ans

c++代码

#include<iostream>#include<stdio.h>#include<deque>using namespace std;deque<int>q;int main(){    int i, x, ans = -999,n;    scanf("%d",&n);    for(i=1;i<=n;i++)    {        scanf("%d",&x);        while(!q.empty()&&q.back()<=x)        {            ans = max(ans,q.back()^x);            q.pop_back();        }        if(q.size()>1) ans= max(ans,q.back()^x);        q.push_back(x);    }    printf("%d",ans);}