Dr. Evil Underscores
Today, as a friendship gift, Bakry gave Badawy nn integers a1,a2,…,ana1,a2,…,an and challenged him to choose an integer XX such that the value max1≤i≤n(ai⊕X)max1≤i≤n(ai⊕X) is minimum possible, where ⊕⊕ denotes the bitwise XOR operation.
As always, Badawy is too lazy, so you decided to help him and find the minimum possible value of max1≤i≤n(ai⊕X)max1≤i≤n(ai⊕X).
Input
The first line contains integer nn (1≤n≤1051≤n≤105).
The second line contains nn integers a1,a2,…,ana1,a2,…,an (0≤ai≤230−10≤ai≤230−1).
Output
Print one integer — the minimum possible value of max1≤i≤n(ai⊕X)max1≤i≤n(ai⊕X).
链接:http://codeforces.com/contest/1285/problem/D
题意:寻找x与数组a异或,求异或后数组内最大值,使得最大值最小。
题解:分治 字典树 dp(dp待补)
#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
using ll = long long;
ll solve(vector<ll> a,int b)
{
if(b==-1)return 0;
ll temp = 1ll<<b;
vector<ll> l, r;
for(auto i:a)
{
if(i<temp)l.push_back(i);
else r.push_back(i-temp);
}
if(l.empty())return solve(r,b-1);
if(r.empty())return solve(l,b-1);
return min(solve(l,b-1),solve(r,b-1))+temp;
}
int main(){
int n;
cin>>n;
vector<ll> a(n);
for(int i=0;i<n;i++)
cin>>a[i];
sort(a.begin(),a.end());
cout<<solve(a,32)<<endl;
return 0;
}