1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
| #include <bits/stdc++.h>
const int MaxN = 50;
const double delta = 0.995;
int n, m;
int a[MaxN], f[MaxN];
double sum[MaxN], aver = 0, ans = 1e18;
inline int read()
{
int x = 0, f = 1;
char ch = getchar();
while(ch > '9' || ch < '0')
{
if(ch == '-')
f = 0;
ch = getchar();
}
while(ch <= '9' && ch >= '0')
x = (x << 1) + (x << 3) + (ch ^ 48), ch = getchar();
return f ? x : (-x);
}
inline double calc()
{
double tmp = 0;
for (int i = 1; i <= m; i++)
tmp += (sum[i] - aver) * (sum[i] - aver);
return tmp;
}
void sa()
{
memset(sum, 0, sizeof(sum));
double tmp = 0;
for(int i = 1; i <= n; i++)
f[i] = rand() % m + 1, sum[f[i]] += a[i];
for(int i = 1; i <= m; i++)
tmp += (sum[i] - aver) * (sum[i] - aver);
double t = 10000000;
while(t > 1e-14)
{
int x = rand() % n + 1, y = rand() % n + 1;
while(f[x] == f[y])
x = rand() % n + 1, y = rand() % n + 1;
sum[f[x]] -= a[x];
sum[f[x]] += a[y];
sum[f[y]] += a[x];
sum[f[y]] -= a[y];
double now = calc();
if ((now < tmp) || (exp((now - tmp) / t) * RAND_MAX < rand()))
tmp = now, std::swap(f[x], f[y]);
else
sum[f[x]] += (a[x] - a[y]), sum[f[y]] += (a[y] - a[x]);
t *= delta;
}
if(tmp < ans)
ans = tmp;
}
int main()
{
srand(time(NULL));
n = read(), m = read();
for(int i = 1; i <= n; i++)
a[i] = read(), aver += a[i];
aver /= m;
for(int i = 1; i <= 500; i++)
sa();
printf("%.2lf", sqrt(ans / m));
return 0;
}
|