题解 | 绕距

#include <stdio.h>
#include <math.h>

int main() {
    double a,b,c,d;
    scanf("%lf %lf",&a,&b);
    scanf("%lf %lf",&c,&d);
    double e = sqrt((a-c)*(a-c)+(b-d)*(b-d));
    double m = fabs(a-c) + fabs(b-d);
    double f = round(fabs(e-m)*1e15)/1e15;
    printf("%.18lf",f);
    return 0;
}