大力猜结论：所有位于定义域内的数的取值的概率都相等，所以答案就是平均数。
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| #include <iostream>
#include <cstdio>
using namespace std;
typedef long long ll;
int n, r, a[262155], uu, vv;
ll sum;
int main(){
cin>>n>>r;
for(int i=0; i<(1<<n); i++){
scanf("%d", &a[i]);
sum += a[i];
}
printf("%.12f\n", (double)sum/(1<<n));
while(r--){
scanf("%d %d", &uu, &vv);
sum -= a[uu];
a[uu] = vv;
sum += a[uu];
printf("%.12f\n", (double)sum/(1<<n));
}
return 0;
}
|