二分抽签算法分析

限制条件:   1≤n ≤ 50;   1 ≤ m ≤ 10^8;   1 ≤ Ki ≤ 10^8

输入样例： 3 10 1 3 5             (格式-n,m, k1,k2,..kn)
输出样例：YES

输入样例：3 9 1 3 5 
输出样例：NO
*/


#include<algorithm>

using namespace std;

int n, m, i, j;

int kk[1000000];//开大点防止爆掉        
int (int b){
    int left = 0, right = n*n-1;
    while(left < right){
        int k = left+(right-left)/2;
        if(kk[k] == b)
            return 1;
        if( m >kk[k])
            left = k+1;
        else
            right = k;
                
    }

    return 0;
}

int main(){
    
    cin >> n >> m;
    int a[n];
    for(i = 0; i < n; i++){
        cin >> a[i];
    }
    for ( i=0; i < n; i++)
        for  ( j=0; j < n; j++)
            kk[i*n + j] = a[i]+a[j];//枚举组合
    sort(kk, kk+n*n); 
    for(i = 0; i < n; i++)
        for(j = 0; j < n; j++){
                if( bs(m-a[i]-a[j]) ){
                    cout << "YES";
                    return 0;
                }
            } 
        
        
    cout << "NO";
    return 0;
}