Pick-up sticks
Stan has n sticks of various length. He throws them one at a time on the floor in a random way. After finishing throwing, Stan tries to find the top sticks, that is these sticks such that there is no stick on top of them. Stan has noticed that the last thrown stick is always on top but he wants to know all the sticks that are on top. Stan sticks are very, very thin such that their thickness can be neglected.
Input
Input consists of a number of cases. The data for each case start with 1 <= n <= 100000, the number of sticks for this case. The following n lines contain four numbers each, these numbers are the planar coordinates of the endpoints of one stick. The sticks are listed in the order in which Stan has thrown them. You may assume that there are no more than 1000 top sticks. The input is ended by the case with n=0. This case should not be processed.
Output
For each input case, print one line of output listing the top sticks in the format given in the sample. The top sticks should be listed in order in which they were thrown.
The picture to the right below illustrates the first case from input.
Sample Input
5
1 1 4 2
2 3 3 1
1 -2.0 8 4
1 4 8 2
3 3 6 -2.0
3
0 0 1 1
1 0 2 1
2 0 3 1
0
Sample Output
Top sticks: 2, 4, 5.
Top sticks: 1, 2, 3.
Hint
Huge input,scanf is recommended.
Source
题目类型：线段相交
算法分析：直接双重枚举判断每个线段是否与被后边的线段相交即可
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/************************************************* Author :supermaker Created Time :2016/1/29 20:44:22 File Location :C:\Users\abcd\Desktop\TheEternalPoet **************************************************/ #pragma comment(linker, "/STACK:102400000,102400000") #include <set> #include <bitset> #include <list> #include <map> #include <stack> #include <queue> #include <deque> #include <string> #include <vector> #include <ios> #include <iostream> #include <fstream> #include <sstream> #include <iomanip> #include <algorithm> #include <utility> #include <complex> #include <numeric> #include <functional> #include <cmath> #include <ctime> #include <climits> #include <cstdarg> #include <cstdio> #include <cstdlib> #include <cstring> #include <cctype> #include <cassert> using namespace std; #define CFF freopen ("aaa.txt", "r", stdin) #define CPPFF ifstream cin ("aaa.txt") #define DB(ccc) cout << #ccc << " = " << ccc << endl #define PB push_back #define MP(A, B) make_pair(A, B) typedef long long LL; typedef unsigned long long ULL; typedef double DB; typedef pair <int, int> PII; typedef pair <int, bool> PIB; const int INF = 0x7F7F7F7F; const int MOD = 1e9 + 7; const double EPS = 1e-10; const double PI = 2 * acos (0.0); const int maxn = 1e5 + 66; int sgn (double val) { if (fabs (val) < EPS) return 0; else if (val < 0) return -1; return 1; } struct Point { double x, y; Point () {} Point (double xx, double yy) : x (xx), y (yy) {} Point operator - (const Point &a) const { return Point (x - a.x, y - a.y); } double operator ^ (const Point &a) const { return x * a.y - y * a.x; } double operator * (const Point &a) const { return x * a.x + y * a.y; } }; struct Line { Point s, e; Line () {} Line (Point ss, Point ee) : s (ss), e (ee) {} }; int n; Line l[maxn]; vector <int> res; bool Inter (Line l1, Line l2) { return max (l1.s.x, l1.e.x) >= min (l2.s.x, l2.e.x) && max (l2.s.x, l2.e.x) >= min (l1.s.x, l1.e.x) && max (l1.s.y, l1.e.y) >= min (l2.s.y, l2.e.y) && max (l2.s.y, l2.e.y) >= min (l1.s.y, l1.e.y) && sgn ((l2.s - l1.e) ^ (l1.s - l1.e)) * sgn ((l2.e - l1.e) ^ (l1.s - l1.e)) <= 0 && sgn ((l1.s - l2.e) ^ (l2.s - l2.e)) * sgn ((l1.e - l2.e) ^ (l2.s - l2.e)) <= 0; } int main() { //CFF; //CPPFF; while (scanf ("%d", &n) != EOF) { if (n == 0) break; for (int i = 1; i <= n; i++) scanf ("%lf%lf%lf%lf", &l[i].s.x, &l[i].s.y, &l[i].e.x, &l[i].e.y); res.clear (); for (int i = 1; i <= n; i++) { bool is_over = false; for (int j = i + 1; j <= n; j++) if (Inter (l[i], l[j])) { is_over = true; break; } if (!is_over) res.push_back (i); } printf ("Top sticks:"); for (int i = 0; i < res.size (); i++) { if (i == res.size () - 1) printf (" %d.\n", res[i]); else printf (" %d,", res[i]); } } return 0; } |
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