题解

#include <cstdio>
#include <cmath>
using namespace std;
float dis(float x1,float y1,float x2,float y2){
    return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}int main(){
    float x1,x2,x3,y1,y2,y3;
    scanf("%f%f%f%f%f%f",&x1,&y1,&x2,&y2,&x3,&y3);
    float s1 = dis(x1,y1,x2,y2),s2 = dis(x2,y2,x3,y3),s3 = dis(x1,y1,x3,y3);
    printf("%.2f",s1+s2+s3);
    return 0;
}