二分查找的典型应用，寻找虚无的值代入测试

1 #include 
     
       2 #define _for(i,a,b) for(int i = (a);i < b;i ++) 3 typedef long long ll; 4 using namespace std; 5 inline ll read() 6 { 7     ll ans = 0; 8     char ch = getchar(), last = ' '; 9     while(!isdigit(ch)) last = ch, ch = getchar();10     while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar();11     if(last == '-') ans = -ans;12     return ans;13 }14 inline void write(ll x)15 {16     if(x < 0) x = -x, putchar('-');17     if(x >= 10) write(x / 10);18     putchar(x % 10 + '0');19 }20 ll n,k; 21 ll a[200006];22 bool C(ll d)23 {24     ll line = a[n/2]+d;25     ll tmpk = k;26     tmpk -= d;27     _for(i,n/2+1,n)28         if(a[i]
      
       =0;33 }34 ll solve()35 {36     ll lb = 0,ub = 1000000002;37     while(ub - lb > 1)38     {39         ll mid =  lb+(ub-lb)/2;40         if(C(mid)) lb = mid;41         else ub = mid;42     }43     return lb;44 }45 int main()46 {47     n = read(),k = read();48     _for(i,0,n)49         a[i] = read();50     sort(a,a+n);51     ll rnt = solve();52     write(rnt+a[n/2]);53     return 0;54 }