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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} ]

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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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