数三角

数三角
https://ac.nowcoder.com/acm/contest/3003/D

先使用数组记录任意两个点所连的边，再进行钝角判断
a^2+b^2<c^2

#pragma warning (disable :4996)
#include <iostream>
#include <cstdio>
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 2e5 + 10;

ll San[550][550];
struct Point {
    ll x, y;
};
ll sum = 0;
ll a, b, c;
void Max() {
    if (a > b) {
        ll tmp = a;
        a = b, b = tmp;
    }
    if (a > c) {
        ll tmp = a;
        a = c, c = tmp;
    }
    if (b > c) {
        ll tmp = b;
        b = c, c = tmp;
    }
}
int main()
{
    int n;
    ll x, y;
    Point S[550];
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) {
        scanf("%lld %lld", &x, &y);
        S[i].x = x, S[i].y = y;
    }
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            if (i == j)
                San[i][j] = 0;
            else
                San[i][j] = (S[i].x - S[j].x) * (S[i].x - S[j].x) + (S[i].y - S[j].y) * (S[i].y - S[j].y);
        }
    }
    for (int i = 1; i <= n; i++) {
        for (int j = i + 1; j <= n; j++) {
            for (int k = j + 1; k <= n; k++) {
                a = San[i][j];
                b = San[i][k];
                c = San[j][k];
                Max();

                if (b + a < c) {

                    if ((S[i].y - S[j].y) * 1.0 / (S[i].x - S[j].x) * 1.0 == (S[i].y - S[k].y) * 1.0 / (S[i].x - S[k].x) * 1.0)
                        continue;
                    sum++;
                }

            }
        }
    }
    cout << sum << endl;
}