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

Code mẫu của happyboy99x

#include<algorithm>
#include<cassert>
#include<complex>
#include<vector>
#include<cstdio>
using namespace std;

typedef complex<long long> Point;

long long cross(const Point &a, const Point &b) {
    return imag(conj(a) * b);
}

struct Ball {
    Point pos;
    int color, id;

    Ball(const Point &_pos, int _color, int _id):
        pos (_pos), color (_color), id (_id) {}

    bool operator < (const Ball &b) const {
        long long crs = cross(pos, b.pos);
        return crs == 0 ? norm(pos) < norm(b.pos) : crs > 0;
    }

    bool isBad() const {
        return imag(pos) < 0 || (imag(pos) == 0 && real(pos) <= 0);
    }
};

int main() {
    vector<Ball> balls;
    int n; scanf("%d", &n);
    for(int i = 0; i < 2 * n; ++i) {
        int x, y; scanf("%d %d", &x, &y);
        balls.push_back(Ball(Point(x, y), i < n ? 0 : 1, i));
    }
    n *= 2;
    for(int root = 0; root < n; ++root) {
        vector<Ball> upper;
        for(int i = 0; i < n; ++i) {
            Ball x = balls[i];
            x.pos -= balls[root].pos;
            if(!x.isBad()) upper.push_back(x);
        }
        sort(upper.begin(), upper.end());
        int m = upper.size();
        for(int i = 0; i < m; ) {
            int j = i;
            while(j < m && cross(upper[i].pos, upper[j].pos) == 0) ++j;
            vector<int> ballByType[2];
            for(int k = i; k < j; ++k)
                ballByType[upper[k].color].push_back(upper[k].id);
            if(!ballByType[0].empty() && !ballByType[1].empty()) {
                printf("%d %d %d\n", root + 1, ballByType[0].front() + 1, ballByType[1].front() + 1);
                return 0;
            }
            int need = balls[root].color ^ 1;
            if(ballByType[need].size() >= 2) {
                printf("%d %d %d\n", root + 1, ballByType[need][0] + 1, ballByType[need][1] + 1);
                return 0;
            }
            i = j;
        }
    }
    printf("-1\n");
    return 0;
}

Code mẫu của ladpro98

#include <bits/stdc++.h>
#define ii pair<int, int>
#define iii pair<ii, int>
#define dii pair<long double, ii>
#define X first
#define Y second
using namespace std;
const int N = 2222;
const int green = 1;
const int red = 2;
const long double eps = 1e-13;
iii a[N];
dii vec[N * N];
int n, m, nv;
int point[5];

int gcd(int a, int b) {
    if (b == 0) return a;
    if (a % b == 0) return b;
    return gcd(b, a % b);
}

int main()
{
    scanf("%d\n", &n); m = 0;
    int i, j, x, y, g;
    for(i=1; i<=n; i++) {
        scanf("%d %d\n", &x, &y);
        a[++m] = iii(ii(x, y),  green);
    }
    for(i=1; i<=n; i++) {
        scanf("%d %d\n", &x, &y);
        a[++m] = iii(ii(x, y), red);
    }
    for(i=1; i<=m; i++) for(j=i+1; j<=m; j++)
    if (i != j) {
        vec[++nv] = dii((long double)(a[i].X.X - a[j].X.X) / (a[i].X.Y - a[j].X.Y),
                        ii(i, j));
    }
    sort(vec+1, vec+1+nv);
    dii v1, v2; int product; long double diff;
    long long x1, x2, y1, y2;
    for(i=1; i<nv; i++) {
        v1 = vec[i]; v2 = vec[i+1];
        diff = abs(v1.X - v2.X);
        if (diff < eps) {
            x1 = a[v1.Y.X].X.X - a[v1.Y.Y].X.X;
            x2 = a[v1.Y.X].X.Y - a[v1.Y.Y].X.Y;
            y1 = a[v2.Y.X].X.X - a[v2.Y.Y].X.X;
            y2 = a[v2.Y.X].X.Y - a[v2.Y.Y].X.Y;
            if (x1 * y2 != x2 * y1) continue;
            point[1] = v1.Y.X; point[2] = v1.Y.Y;
            point[3] = v2.Y.X; point[4] = v2.Y.Y;
            product = a[v1.Y.X].Y * a[v1.Y.Y].Y * a[v2.Y.X].Y * a[v2.Y.Y].Y;
            if (product != 1 && product != 16) {
                sort(point+1, point+5);
                if (!(point[1] == point[2] || point[2] == point[3] || point[3] == point[4])) continue;
                for(j=1; j<=4; j++)
                    if (point[j] != point[j-1]) printf("%d ", point[j]);
                return 0;
            }
        }
    }
    printf("-1");
    return 0;
}

Code mẫu của RR

#include <bits/stdc++.h>

#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 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

struct Point {
    long long x, y;
    int id, color;

    Point() {}
    Point(long long x, long long y) : x(x), y(y) {}

    Point operator - (Point a) { return Point(x-a.x, y-a.y); }
} a[2011], b[2011];
int n, cur;

int ccw(Point a, Point b, Point c) {
    b = b - a; c = c - a;
    long long t = b.x*c.y - b.y*c.x;
    if (t == 0) return 0;
    else if (t < 0) return -1;
    else return 1;
}

struct Comp {
    Point pivot;
    bool operator () (const Point &a, const Point &b) {
        return ccw(pivot, a, b) == 1;
    }
} comp;

int main() {
    ios :: sync_with_stdio(false);
    cin >> n; n *= 2;
    FOR(color,0,1)
        FOR(i,1,n/2) {
            int u = color*n/2 + i;
            cin >> a[u].x >> a[u].y;
            a[u].id = u;
            a[u].color = color;
        }

    FOR(i,1,n) {
        int cur = 0;
        FOR(j,1,n) if (j != i)
        if (a[j].y > a[i].y || (a[j].y == a[i].y && a[j].x > a[i].x)) {
            b[++cur] = a[j];
        }
        comp.pivot = a[i];
        sort(b+1, b+cur+1, comp);

        FOR(j,1,cur-1) {
            int sum = a[i].color + b[j].color + b[j+1].color;
            if (ccw(a[i], b[j], b[j+1]) == 0 && sum && sum < 3) {
                cout << a[i].id << ' ' << b[j].id << ' ' << b[j+1].id << endl;
                return 0;
            }
        }
    }
    cout << -1 << endl;
    return 0;
}