codeforces-1201 C Maximum Median

二分查找的典型应用，寻找虚无的值代入测试

 1 #include <bits/stdc++.h>
 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]<line)
29             tmpk -= line-a[i];
30         else
31             break;
32     return tmpk>=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 }