有没有神犇解释一下
by dbjbjbj @ 2022-10-12 21:03:40
1.5+1.5+1.5>4.5?
by dbjbjbj @ 2022-10-12 21:04:36
显然的，当你的点在三角形外时 `s>s1+s2+s3`
by reveal @ 2022-10-12 21:04:43
玄学~~精度~~90分
```cpp
#include<bits/stdc++.h>
using namespace std;
struct node{
int x,y;
}a[4],b;
inline int read() {
int f = 1, x = 0;
char ch = getchar();
while (ch < '0' || ch > '9') {
if (ch == '-') {
f = -1;
}
ch = getchar();
}
while (ch >= '0' && ch <= '9') {
x = (x << 3) + (x << 1) + (ch ^ 48);
ch = getchar();
}
return ~f ? x : -x;
}
inline void write(int x) {
if (x < 0) {
putchar('-');
x = -x;
}
if (x > 9) {
write(x / 10);
putchar(x % 10 + '0');
}
else
putchar(x + '0');
return;
}
double dis(node a,node b){
return sqrt(pow(a.x-b.x,2)+pow(a.y-b.y,2));
}
double S(node a,node b,node c){
double ab=dis(a,b),bc=dis(b,c),ac=dis(a,c);
double p=(ab+bc+ac)/2;
return sqrt(p*(p-ab)*(p-bc)*(p-ac));
}
int main(){
// ios::sync_with_stdio(false);
a[1].x=read(),a[1].y=read();
a[2].x=read(),a[2].y=read();
a[3].x=read(),a[3].y=read();
b.x=read(),b.y=read();
double s=S(a[1],a[2],a[3]),s1=S(a[1],a[2],b),s2=S(a[1],a[3],b),s3=S(a[2],a[3],b);
// cout<<s<<' '<<s1<<' '<<s2<<' '<<s3;
if(!s1||!s2||!s3){
if(s1==s||s2==s||s3==s){
putchar('4');
}
else{
putchar('3');
}
}
else{
// cout<<s1+s2+s3;
if(s1+s2+s3-s>0.0000001){
// cout<<s<<' '<<s1<<' '<<s2<<' '<<s3<<'\n';
putchar('2');
}
else{
putchar('1');
}
}
// cin.tie(0);
return 0;
}
```
by dbjbjbj @ 2022-10-12 21:10:17
实际上，因为是整点多边形，可以使用叉积计算面积避免浮点数
by reveal @ 2022-10-12 21:17:53
自己输出多几位应该就会发现不是1.5，也不是4.5
by _YyD_ @ 2023-02-23 15:18:01