POJ 2826 An Easy Problem?!
这题的恶心程度一流。
卡精度貌似丧心病狂。。
WA了一版。
最后G++过不了，C++过的。
考虑好DISCUSS中的情况基本就行了、
#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <algorithm>#include <cstdlib>#include <cmath>#include <map>#include <sstream>#include <queue>#include <vector>#define MAXN 100005#define MAXM 211111#define eps 1e-8#define INF 50000001using namespace std;inline int dblcmp(double d){ if(fabs(d) < eps) return 0; return d > eps ? 1 : -1;}struct point{ double x, y; point(){} point(double _x, double _y): x(_x), y(_y) {} void input() { scanf("%lf%lf", &x, &y); } bool operator ==(point a)const { return dblcmp(a.x - x) == 0 && dblcmp(a.y - y) == 0; } point sub(point p) { return point(x - p.x, y - p.y); } double dot(point p) { return x * p.x + y * p.y; } double det(point p) { return x * p.y - y * p.x; } double distance(point p) { return hypot(x - p.x, y - p.y); }};struct line{ point a, b; line(){} line(point _a, point _b){ a = _a; b = _b;} void input() { a.input(); b.input(); } int segcrossseg(line v) { int d1 = dblcmp(b.sub(a).det(v.a.sub(a))); int d2 = dblcmp(b.sub(a).det(v.b.sub(a))); int d3 = dblcmp(v.b.sub(v.a).det(a.sub(v.a))); int d4 = dblcmp(v.b.sub(v.a).det(b.sub(v.a))); if ((d1 ^ d2) == -2 && (d3 ^ d4) == -2)return 2; return (d1 == 0 && dblcmp(v.a.sub(a).dot(v.a.sub(b))) <= 0|| d2 == 0 && dblcmp(v.b.sub(a).dot(v.b.sub(b))) <= 0|| d3 == 0 && dblcmp(a.sub(v.a).dot(a.sub(v.b))) <= 0|| d4 == 0 && dblcmp(b.sub(v.a).dot(b.sub(v.b))) <= 0); } point crosspoint(line v) { double a1 = v.b.sub(v.a).det(a.sub(v.a)); double a2 = v.b.sub(v.a).det(b.sub(v.a)); return point((a.x * a2 - b.x * a1) / (a2 - a1), (a.y * a2 - b.y * a1) / (a2 - a1)); }}a, b;void gao(){ point x = a.crosspoint(b); a.b = x; b.b = x; if(dblcmp(point(a.a.sub(a.b)).det(b.a.sub(b.b))) < 0) swap(a, b); if(dblcmp(a.a.y - b.a.y) > 0 && dblcmp(a.a.x - b.a.x) <= 0) { printf("0.00\n"); return; } if(dblcmp(a.a.y - b.a.y) < 0 && dblcmp(a.a.x - b.a.x) <= 0) { printf("0.00\n"); return; } if(dblcmp(a.a.y - b.a.y) < 0) { line tmp = line(a.a, point(-INF, a.a.y)); point z = tmp.crosspoint(b); b.a = z; } else if(dblcmp(a.a.y - b.a.y) > 0) { line tmp = line(b.a, point(INF, b.a.y)); point z = tmp.crosspoint(a); a.a = z; } double ans = point(a.a.sub(a.b)).det(b.a.sub(b.b)) / 2.0; printf("%.2f\n", fabs(ans));}int main(){ int T; scanf("%d", &T); while(T--) { a.input(); b.input(); if(dblcmp(a.a.y - a.b.y) < 0) swap(a.a, a.b); if(dblcmp(b.a.y - b.b.y) < 0) swap(b.a, b.b); if(dblcmp(a.a.sub(a.b).det(b.a.sub(b.b))) == 0) printf("0.00\n"); else if(dblcmp(a.a.y - a.b.y) == 0 || dblcmp(b.a.y - b.b.y) == 0) printf("0.00\n"); else if(a.segcrossseg(b) == 0) printf("0.00\n"); else gao(); } return 0;}