求助，有无佬看看哪里有问题，过90%

#include<iostream>

#include<cmath>

#include<iomanip>

using namespace std;

int main(){

long long n,m,k,t;

cin>>k;

n=k+1;

int arr[100000];

while (n--){

cin>>arr[n];

}

double l=0;

n=0;

while (n<k){

for (m=n+1,t=n+2;t<=k;t++){

if ((arr[m]-arr[n])/(double)(m-n)<(arr[t]-arr[n])/(double)(t-n))

m=t;

}

l+=sqrt((arr[m]-arr[n])*(arr[m]-arr[n])+(m-n)*(m-n));

n=m;

}

cout<<fixed<<setprecision(12)<<l;

}