codeforces 742B - Arpa’s obvious problem and Mehrdad’s terrible solution

B. Arpa’s obvious problem and Mehrdad’s terrible solution

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

There are some beautiful girls in Arpa’s land as mentioned before.

Once Arpa came up with an obvious problem:

Given an array and a number x, count the number of pairs of indices i, j (1 ≤ i < j ≤ n) such that , where  is bitwise xoroperation (see notes for explanation).

 

Immediately, Mehrdad discovered a terrible solution that nobody trusted. Now Arpa needs your help to implement the solution to that problem.

Input

First line contains two integers n and x (1 ≤ n ≤ 105, 0 ≤ x ≤ 105) — the number of elements in the array and the integer x.

Second line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 105) — the elements of the array.

Output

Print a single integer: the answer to the problem.

二分搜索

AC代碼：

 

# include <stdio.h>
# include <vector>
using namespace std;
typedef long long int ll;
int a[100010];
vector<int> vec[100010];
int main(){
	int i, j, k, x, n, temp, s;
	scanf("%d%d", &n, &x);
	for(i=1; i<=n; i++){
		scanf("%d", &a[i]);
		vec[a[i]].push_back(i);
	}
	ll ans=0;
	for(i=1; i<n; i++){
		temp=x^a[i];
		if(temp<100010)
			s=vec[temp].size();
		else
			continue;
		if(s>0){
			int it=lower_bound(vec[temp].begin(), vec[temp].end(), i+1)-vec[temp].begin();
			if(it>s)
			continue;
			if(it!=s){
				ans=ans+s-it;
			}
		}
	}
	printf("%I64d", ans);
	return 0;
}