CodeForces 742B Arpa’s obvious problem and Mehrdad’s terrible solution (暴力枚举)

题意：求定 n 个数，求有多少对数满足，ai^bi = x。

析：暴力枚举就行，n的复杂度。

代码如下：

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <cstdio>
#include <string>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <cstring>
#include <set>
#include <queue>
#include <algorithm>
#include <vector>
#include <map>
#include <cctype>
#include <cmath>
#include <stack>
#define freopenr freopen("in.txt", "r", stdin)
#define freopenw freopen("out.txt", "w", stdout)
using namespace std;

typedef long long LL;
typedef pair<int, int> P;
const int INF = 0x3f3f3f3f;
const double inf = 0x3f3f3f3f3f3f;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int maxn = 1e5 + 5;
const int mod = 1e9 + 7;
const int dr[] = {-1, 1, 0, 0};
const int dc[] = {0, 0, 1, -1};
const char *de[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};
int n, m;
const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
inline int Min(int a, int b){ return a < b ? a : b; }
inline int Max(int a, int b){ return a > b ? a : b; }
inline LL Min(LL a, LL b){ return a < b ? a : b; }
inline LL Max(LL a, LL b){ return a > b ? a : b; }
inline bool is_in(int r, int c){
    return r >= 0 && r < n && c >= 0 && c < m;
}
int a[100005];
int b[100005];

int main(){
    LL n, m;
    while(scanf("%I64d %I64d", &n, &m) == 2){
        for(int i = 0; i < n; ++i)  scanf("%d", a+i);
        memset(b, 0, sizeof b);
        LL ans = 0;
//        if(m == 0){
//            for()
//            continue;
//        }
        for(int i = n-1; i >= 0; --i){
            LL t = a[i] ^ m;
            if(t < 100005)  ans += b[t];
            ++b[a[i]];
        }
        cout << ans << endl;
    }
    return 0;
}