#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
double rs, rb;
long long cache[41][41];
long long coef(int n, int r) {
if (r == 0 || n == r) return 1;
long long& ret = cache[n][r];
if (ret != -1) return ret;
ret = coef(n-1, r-1) + coef(n, r-1);
return ret;
}
int main() {
long long a, b, n, k;
cin >> a >> b >> n >> k;
if (a > b) swap(a, b);
rs = log((double)a*a / (double)(a*a + b*b));
rb = log((double)b*b / (double)(a*a + b*b));
double S0 = log(a*b / 2.0);
int idx = 0;
memset(cache, -1, sizeof(cache));
while (k > coef(n, idx)) {
k -= coef(n, idx);
idx++;
}
for (int i = 0; i < idx; ++i)
S0 += rs;
for (int i = idx; i < n; ++i)
S0 += rb;
printf("%.12f\n", S0);
}
Compilation message
A.cpp: In function ‘int main()’:
A.cpp:26:36: error: ‘memset’ was not declared in this scope
memset(cache, -1, sizeof(cache));
^
