function r = PointToLineSegment3D( S1, S2, Pnt )
% r = PointToLineSegment3D( S1, S2, Pnt )

vx = S1(1)-Pnt(1);
vy = S1(2)-Pnt(2);
% vz = S1(3)-Pnt(3);

ux = S2(1)-S1(1);
uy = S2(2)-S1(2);
% uz = S2(3)-S1(3);

lenSqr= (ux*ux+uy*uy); % +uz*uz
detP= -vx*ux + -vy*uy;

if( detP < 0 )
    r = norm(S1-Pnt,2);

elseif( detP > lenSqr )
    r = norm(S2-Pnt,2);

else
    r = abs(ux*vy-uy*vx)/sqrt(lenSqr);
end
end

X = A+t*(B-A)

0 == (A+t*(B-A) - P)' * (B-A) == (A-P)'*(B-A)+t*norm(B-A)^2

t = (A-P)'*(B-A) / norm(B-A)^2

d = norm(X-P)

d = norm(A+t*(B-A)-P)

function r = PointToLineSegment3D( S1, S2, Pnt )
% r = PointToLineSegment3D( S1, S2, Pnt )

vx = S1(1)-Pnt(1);
vy = S1(2)-Pnt(2);
vz = S1(3)-Pnt(3);

ux = S2(1)-S1(1);
uy = S2(2)-S1(2);
uz = S2(3)-S1(3);

lenSqr= (ux*ux+uy*uy+uz*uz)


detP= -vx*ux + -vy*uy + -vz*uz;

if( detP < 0 )
    r = norm(S1-Pnt,2);

elseif( detP > lenSqr )
    r = norm(S2-Pnt,2);

else
    r =norm( abs(cross((S2-S1),(S1-Pnt)))/sqrt(lenSqr));
end
end

Pnt=[1 1 1];
S1=[0 0 0];
S2=[0 3 3];

vx = S1(1)-Pnt(1);
vy = S1(2)-Pnt(2);
vz = S1(3)-Pnt(3);

ux = S2(1)-S1(1);
uy = S2(2)-S1(2);
uz = S2(3)-S1(3);

lenSqr= (ux*ux+uy*uy+uz*uz)
detP= -vx*ux + -vy*uy + -vz*uz

i1 = uz*vy-uy*vz
j1 = ux*vz-uz*vx
k1 = uy*vx-ux*vy

if( detP < 0 )
    r = norm(S1-Pnt,2)

elseif( detP > lenSqr )
    r = norm(S2-Pnt,2)

else
    r = sqrt(conv(i1,i1)+conv(j1,j1)+conv(k1,k1)) /sqrt(lenSqr)
end

#include<iostream>
#include<math.h>
#include<stdio.h>
#include<vector>
#include<iterator>
#include <iomanip>

using namespace std;
int main()
{

double vx,vy,vz,ux,uy,uz,r=0,lenSqr,detP, c,tmp;
int i;
vector<double>copy;
vector<double>Pnt;
vector<double>S1;
vector<double>S2;

for(i=0; i<9; i++)
{
    cin>>c;
    copy.push_back(c);
}
for(i=0; i<3; i++)
{
    Pnt.insert(Pnt.begin(), copy[i]);
//  cout<<copy[i]<<endl;
}
    copy.erase(copy.begin(),copy.begin()+3);
    copy.shrink_to_fit();
for(i=0; i<3; i++)
{
    S1.insert(S1.begin(), copy[i]);
}
copy.erase(copy.begin(),copy.begin()+3);
copy.shrink_to_fit();
for(i=0; i<3; i++)
{
    S2.insert(S2.begin(), copy[i]);
    copy.erase(copy.begin());
}
copy.shrink_to_fit();



/*
vector<float>Pnt(3,1.0);
//for(i=0; i<3; i++)
//cout<<Pnt[i];

vector<float>S1(3,0.0);
//for(i=0; i<3; i++)
//cout<<S1[i];

vector<float>S2;
S2.insert(S2.begin(), 3.0);
S2.insert(S2.begin(), 3.0);
S2.insert(S2.begin(), 0.0);

//for(int i=0; i<3; i++)
//cout<<S2[i];
//cout<<endl;
*/

vx = S1[0]-Pnt[0];
vy = S1[1]-Pnt[1];
vz = S1[2]-Pnt[2];
//cout<<"V: "<<vx<<vy<<vz<<endl;
ux = S2[0]-S1[0];
uy = S2[1]-S1[1];
uz = S2[2]-S1[2];
//cout<<"U: "<<ux<<uy<<uz<<endl;


lenSqr= (ux*ux+uy*uy+uz*uz);
//cout<<"lenSqr "<<lenSqr<<endl;
detP= (-vx*ux ) + (-vy*uy) + (-vz*uz);
//cout<<"detP "<<detP<<endl;



if( detP < 0 )
{
//  r = norm(S1-Pnt,2)
    for(i=0; i<3; i++)
    {
        tmp=pow((S1[i]-Pnt[i]),2);
        r += tmp;
//      cout<<"r: "<<r;
    }
    r = sqrt(r);
    cout<<fixed<<r;
}

else if( detP > lenSqr )
{
//  r = norm(S2-Pnt,2);
    for(i=0; i<3; i++)
    {
        tmp=pow((S2[i]-Pnt[i]),2);
        r += tmp;
//      cout<<"r: "<<r;
    }
    r = sqrt(r);
    cout<<fixed<<r;
}
//if(detP <= lenSqr || detP>=0)
else
{
//  r =norm( abs(cross((S2-S1),(S1-Pnt)))/sqrt(lenSqr));
    float i1,j1,k1;

i1 = uz*vy-uy*vz;
j1 = ux*vz-uz*vx;
k1 = uy*vx-ux*vy;
//cout<<"I J k: "<<i1<<j1<<k1<<endl;
r=sqrt(pow(i1,2)+pow(j1,2)+pow(k1,2))/sqrt(lenSqr);
cout<<fixed<<r;
}

return 0;
}