Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của flashmt

#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
const double PI = acos(-1.0), EPS = 1e-13;

int main()
{
    double x1, y1, v1, x2, y2, v2, difTheta;
    cin >> x1 >> y1 >> v1 >> x2 >> y2 >> v2;
    double r1 = sqrt(x1 * x1 + y1 * y1), r2 = sqrt(x2 * x2 + y2 * y2);
    v1 /= r1; v2 /= r2;
    double theta1 = atan2(y1, x1), theta2 = atan2(y2, x2);

    if (fabs(v1 - v2) < EPS)
    {
        if (fabs(theta1 - theta2) < EPS) puts("0");
        else puts("-1");
    }
    else
    {
        difTheta = theta2 - theta1;
        if (v1 < v2) difTheta = -difTheta;
        while (difTheta < 0) difTheta += PI * 2;
        printf("%.9lf\n", difTheta / fabs(v1 - v2));
    }
}

Code mẫu của happyboy99x

#include<iostream>
#include<cstdio>
#include<complex>
#include<cmath>
using namespace std;

typedef complex<double> point;

int main() {
    long long xv, xe, yv, ye, vv, ve;
    cin >> xv >> yv >> vv >> xe >> ye >> ve;
    if(xv == 0 && yv == 0) printf("0\n");
    else {
        double alpha1 = arg(point(xv, yv));
        double alpha2 = arg(point(xe, ye));
        double omega1 = vv / abs(point(xv, yv));
        double omega2 = ve / abs(point(xe, ye));
        if(abs(omega1 - omega2) <= 1e-9) {
            if(xv * ye == xe * yv && xv * xe + yv * ye > 0) printf("0\n"); 
            else printf("-1\n");
        } else {
            double res = (alpha1 - alpha2) / (omega2 - omega1);
            double delta = 2 * M_PI / abs(omega2 - omega1);
            while(res < 0) res += delta;
            printf("%.10lf\n", res);
        }
    }
    return 0;
}

Code mẫu của RR

#include <sstream>
#include <iomanip>
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <string>
#include <deque>
#include <complex>

#define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; i--)
#define REP(i,a) for(int i=0,_a=(a); i<_a; i++)
#define FORN(i,a,b) for(int i=(a),_b=(b);i<_b;i++)
#define DOWN(i,a,b) for(int i=a,_b=(b);i>=_b;i--)
#define SET(a,v) memset(a,v,sizeof(a))
#define sqr(x) ((x)*(x))
#define ll long long
#define F first
#define S second
#define PB push_back
#define MP make_pair

#define DEBUG(x) cout << #x << " = "; cout << x << endl;
#define PR(a,n) cout << #a << " = "; FOR(_,1,n) cout << a[_] << ' '; cout << endl;
#define PR0(a,n) cout << #a << " = "; REP(_,n) cout << a[_] << ' '; cout << endl;
using namespace std;

//Buffer reading
int INP,AM,REACHEOF;
const int BUFSIZE = (1<<12) + 17;
char BUF[BUFSIZE+1], *inp=BUF;
#define GETCHAR(INP) { \
    if(!*inp && !REACHEOF) { \
        memset(BUF,0,sizeof BUF);\
        int inpzzz = fread(BUF,1,BUFSIZE,stdin);\
        if (inpzzz != BUFSIZE) REACHEOF = true;\
        inp=BUF; \
    } \
    INP=*inp++; \
}
#define DIG(a) (((a)>='0')&&((a)<='9'))
#define GN(j) { \
    AM=0;\
    GETCHAR(INP); while(!DIG(INP) && INP!='-') GETCHAR(INP);\
    if (INP=='-') {AM=1;GETCHAR(INP);} \
    j=INP-'0'; GETCHAR(INP); \
    while(DIG(INP)){j=10*j+(INP-'0');GETCHAR(INP);} \
    if (AM) j=-j;\
}
//End of buffer reading

const long double PI = acos((long double) -1.0);

int main() {
    long double x1, y1, v1, x2, y2, v2;
    while (cin >> x1 >> y1 >> v1 >> x2 >> y2 >> v2) {
        long double a1 = atan2(y1, x1), a2 = atan2(y2, x2);
        long double r1 = sqrt(x1*x1 + y1*y1), r2 = sqrt(x2*x2 + y2*y2);

        v1 /= r1; v2 /= r2;

        if (fabs(a1 - a2) < 1e-8) puts("0");
        else if (fabs(v1 - v2) < 1e-8) puts("-1");
        else {
            long double diff = a2 - a1;
            if (v1 < v2) diff = -diff;
            while (diff < 0) diff += 2 * M_PI;
            cout << (fixed) << setprecision(9) << diff / fabs(v1 - v2) << endl;
        }
    }
    return 0;
}

Code mẫu của skyvn97

#include<cstdio>
#include<cmath>
#define EPS   1e-9
#define PI   acos(-1.0)
double X1,Y1,X2,Y2;
double V1,V2,W1,W2;
double A1,A2,DA;
double omg(const double &x,const double &y) {
    if (fabs(y)<=EPS && x-EPS>0) return (0.0);
    if (fabs(y)<=EPS && x+EPS<0) return (PI);   
    if (fabs(x)<=EPS && y-EPS>0) return (PI/2.0);
    if (fabs(x)<=EPS && y+EPS<0) return (3.0*PI/2.0);
    if (x-EPS>0 && y-EPS>0) return (atan(y/x));
    if (x+EPS<0 && y-EPS>0) return (PI-atan(-y/x));
    if (x+EPS<0 && y+EPS<0) return (PI+atan(y/x));
    if (x-EPS>0 && y+EPS<0) return (2.0*PI-atan(-y/x));
}
void process(void) {
    scanf("%lf",&X1);
    scanf("%lf",&Y1);
    scanf("%lf",&V1);
    scanf("%lf",&X2);
    scanf("%lf",&Y2);
    scanf("%lf",&V2);
    A1=omg(X1,Y1);
    A2=omg(X2,Y2);
    if (fabs(A1-A2)<=EPS) {
        printf("0.00000000");
        return;
    }
    W1=V1/hypot(X1,Y1);
    W2=V2/hypot(X2,Y2);
    if (W1>W2+EPS) {
        if (A2>A1+EPS) DA=A2-A1;
        else DA=2.0*PI-A1+A2;
        printf("%.8lf",DA/fabs(W1-W2));
        return;
    }
    if (W2>W1+EPS) {
        if (A1>A2+EPS) DA=A1-A2;
        else DA=2.0*PI-A2+A1;
        printf("%.8lf",DA/fabs(W2-W1));
        return;
    }
    printf("-1");   
}
int main(void) {
    process();
    return 0;
}