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[ s = \sqrt{\frac{1}{n} \sum_{i=1}^{n} \left(b_i - \frac{1}{n} \sum_{i=1}^{n} b_i \right)^2} ]

???( s ) ?????( b_i ) ?????????( n ) ?????????

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C++??

#include 
   
    
using namespace std;
typedef long long LL;
int n;
LL S;
double ans = 0.0;
double avg = 1.0 * S / n;
LL *a = new LL[n];
void work() {
    scanf("%d %lld", &n, &S);
    ans = 0.0;
    avg = 1.0 * S / n;
    LL *a = new LL[n];
    for (int i = 0; i < n; ++i) {
        scanf("%lld", &a[i]);
    }
    // ?????
    double sum = 0.0;
    for (int i = 0; i < n; ++i) {
        double diff = a[i] - avg;
        sum += diff * diff;
    }
    ans = sqrt(sum / n);
    printf("%.4f", ans);
}
   

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