Add a bunch of other problems

Educational Codeforces Round 41 (Rated for Div. 2)/D. Pair Of Lines.cpp

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+/* Problem URL: https://codeforces.com/contest/961/problem/D */
+
+#include <bits/stdc++.h>
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+
+using namespace std;
+using namespace __gnu_pbds;
+
+template <class T, class comp = less<>>
+using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (int i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
+
+#define repv(i, v) for (auto &i : (v))
+#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
+#define sortv(v) sort(v.begin(), v.end())
+#define all(v) (v).begin(), (v).end()
+
+using vi = vector<int>;
+using vvi = vector<vi>;
+using vvvi = vector<vvi>;
+using vvvvi = vector<vvvi>;
+
+using ll = long long;
+
+using vl = vector<ll>;
+using vvl = vector<vl>;
+using vvvl = vector<vvl>;
+using vvvvl = vector<vvvl>;
+
+template<class v>
+auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
+    os << vec[0];
+    for (size_t i = 1; i < vec.size(); i++) {
+        os << ' ' << vec[i];
+    }
+    os << '\n';
+    return os;
+}
+
+template<class v>
+auto operator>>(istream &is, vector<v> &vec)->istream& {
+    for (auto &i : vec) {
+        is >> i;
+    }
+    return is;
+}
+
+template<class v>
+auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
+    for (auto &i : vec) {
+        os << i[0];
+        for (size_t j = 1; j < i.size(); j++) {
+            os << ' ' << i[j];
+        }
+        os << '\n';
+    }
+    return os;
+}
+
+template<class v>
+auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
+    for (auto &i : vec) {
+        for (auto &j : i) {
+            is >> j;
+        }
+    }
+    return is;
+}
+
+// Geometria
+
+typedef long long ld;
+const ld DINF = 1e18;
+const ld pi = acos(-1.0);
+const ld eps = 1e-9;
+
+#define sq(x) ((x)*(x))
+
+bool eq(ld a, ld b) {
+	return abs(a - b) <= eps;
+}
+
+struct pt { // ponto
+	ld x, y;
+	pt(ld x_ = 0, ld y_ = 0) : x(x_), y(y_) {}
+	bool operator < (const pt p) const {
+		if (!eq(x, p.x)) return x < p.x;
+		if (!eq(y, p.y)) return y < p.y;
+		return 0;
+	}
+	bool operator == (const pt p) const {
+		return eq(x, p.x) and eq(y, p.y);
+	}
+	pt operator + (const pt p) const { return pt(x+p.x, y+p.y); }
+	pt operator - (const pt p) const { return pt(x-p.x, y-p.y); }
+	pt operator * (const ld c) const { return pt(x*c  , y*c  ); }
+	pt operator / (const ld c) const { return pt(x/c  , y/c  ); }
+	ld operator * (const pt p) const { return x*p.x + y*p.y; }
+	ld operator ^ (const pt p) const { return x*p.y - y*p.x; }
+	friend istream& operator >> (istream& in, pt& p) {
+		return in >> p.x >> p.y;
+	}
+};
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int n;
+    cin >> n;
+
+    if (n <= 3) {
+        cout << "YES\n";
+        return 0;
+    }
+
+    V<pt> a(n);
+    cin >> a;
+
+    V<bool> group(n);
+    V<bool> invalid(n);
+
+    auto iscol = [&](pt a, pt b, pt c) {
+        return (b.y - a.y) * (c.x - b.x) == (c.y - b.y) * (b.x - a.x);
+    };
+
+    auto check = [&]() {
+        int first = 0;
+        while (group[first]) {
+            first++;
+        }
+
+        int second = first + 1;
+        while (group[second]) {
+            second++;
+        }
+
+        rep(i, n) {
+            if (group[i]) {
+                continue;
+            }
+
+            if (!iscol(a[first], a[second], a[i])) {
+                return false;
+            }
+        }
+
+        return true;
+    };
+
+    int c = 0;
+
+    rep(i, n) {
+        if (iscol(a[0], a[1], a[i])) {
+            group[i] = true;
+        } else {
+            c++;
+        }
+    }
+
+    if (c <= 2 || check()) {
+        cout << "YES\n";
+        return 0;
+    }
+
+    fill(all(group), false);
+    c = 0;
+    rep(i, n) {
+        if (iscol(a[0], a[2], a[i])) {
+            group[i] = true;
+        } else {
+            c++;
+        }
+    }
+
+    if (c <= 2 || check()) {
+        cout << "YES\n";
+        return 0;
+    }
+
+    fill(all(group), false);
+    c = 0;
+    rep(i, n) {
+        if (iscol(a[1], a[2], a[i])) {
+            group[i] = true;
+        } else {
+            c++;
+        }
+    }
+
+    if (c <= 2 || check()) {
+        cout << "YES\n";
+        return 0;
+    }
+
+    cout << "NO\n";
+}