hdu2578(sort ＋ 二分)

思路：先sort一下，，，要找a + b = k,那么就枚举a二分查找b，然后就是判重；

点击题目链接

/*****************************************
Author      :Crazy_AC(JamesQi)
Time        :2015
File Name   :找两个数,a + b = k,枚举a，二分查找b；
*****************************************/
// #pragma comment(linker, "/STACK:1024000000,1024000000")
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <sstream>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <vector>
#include <map>
#include <set>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include <limits.h>
using namespace std;
#define MEM(a,b) memset(a,b,sizeof a)
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int,int> ii;
const int inf = 1 << 30;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
inline int Readint(){
	char c = getchar();
	while(!isdigit(c)) c = getchar();
	int x = 0;
	while(isdigit(c)){
		x = x * 10 + c - '0';
		c = getchar();
	}
	return x;
}
int a[100050];
int bin(int x,int n){
	int low = 0,high = n - 1;
	while(low <= high){
		int mid = (low + high) >> 1;
		if (x < a[mid]) high = mid - 1;
		else if (x > a[mid])
			low = mid + 1;
		else return 1;//a[mid] == x;
	}
	return 0;//Not find;
}
int main()
{	
	// freopen("in.txt","r",stdin);
	// freopen("out.txt","w",stdout);
	int t;
	int n,k;
	scanf("%d",&t);
	while(t--){
		bool flag = true;
		scanf("%d%d",&n,&k);
		int ans = 0;
		for (int i = 0;i < n;i++)
			scanf("%d",&a[i]);
		sort(a,a + n);
		for (int i = 0;i < n;i++){
			if (bin(k - a[i],n)){
				ans++;
				if (i != 0 && a[i] == a[i - 1])//判重；
					ans--;
			}
		}
		printf("%d\n",ans);
	}
	return 0;
}