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QOJ
ID | 题目 | 提交者 | 结果 | 用时 | 内存 | 语言 | 文件大小 | 提交时间 | 测评时间 |
---|---|---|---|---|---|---|---|---|---|
#622913 | #7906. Almost Convex | clouds_ | WA | 1ms | 7744kb | C++11 | 3.4kb | 2024-10-09 08:29:07 | 2024-10-09 08:29:08 |
Judging History
answer
#include <bits/stdc++.h>
using namespace std;
#define ios ios::sync_with_stdio(false), cin.tie(nullptr)
#define int long long
#define ll long long
#define int128 __int128
#define ull unsigned long long
#define endl "\n"
#define x first
#define y second
#define pi acos(-1)
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
const double eps = 1e-6;
const int N = 1e6 + 10, M = 1010, INF = 0x3f3f3f3f;
const int mod = 998244353;
pii a[N];
pii p[N];
int n, top, stk[N];
bool used[N];
vector<pii> v;
pii operator-(pii a, pii b)
{
return {a.x - b.x, a.y - b.y};
}
int operator*(pii a, pii b)
{
return a.x * b.y - a.y * b.x;
}
int area(pii a, pii b, pii c)
{
return (b - a) * (c - a); // 向量的叉积
}
int lens(pii a, pii b) // 两点间距离
{
int dx = a.x - b.x;
int dy = a.y - b.y;
return dx * dx + dy * dy;
}
void andrew()
{
sort(p, p + n);
for (int i = 0; i < n; i++)
{
while (top >= 2 && area(p[stk[top - 2]], p[stk[top - 1]], p[i]) <= 0)
{
if (area(p[stk[top - 2]], p[stk[top - 1]], p[i]) < 0)
used[stk[top - 1]] = 0;
top--;
}
stk[top++] = i;
used[i] = 1;
}
used[0] = 0;
for (int i = n - 1; i >= 0; i--)
{
if (used[i])
continue;
while (top >= 2 && area(p[stk[top - 2]], p[stk[top - 1]], p[i]) <= 0)
{
top--;
v.push_back(p[stk[top]]); // 非凸包的点
}
stk[top++] = i;
}
top--;
}
pii O;
double cross(double x1, double y1, double x2, double y2)
{
return (x1 * y2 - x2 * y1);
}
double compare(pii a, pii b, pii c) // 计算极角
{
return cross((b.x - a.x), (b.y - a.y), (c.x - a.x), (c.y - a.y));
}
int cmp2(piii a, piii b)
{
pii c = O; // 原点
if (compare(c, a.x, b.x) == 0) // 计算叉积,函数在上面有介绍,如果叉积相等,按照X从小到大排序
return a.x.x < b.x.x;
else
return compare(c, a.x, b.x) > 0;
}
void solve()
{
cin >> n;
for (int i = 0; i < n; i++)
{
cin >> p[i].x >> p[i].y;
used[i] = 0;
}
used[n] = 0;
andrew();
for (int i = 0; i < top; i++)
a[i] = p[stk[i]];
n = top;
int ans = 0;
for (int i = 0; i < v.size(); i++)
{
O = v[i];
vector<piii> q;
q.push_back({v[i], 0});
for (int l = 0; l < n; l++)
q.push_back({a[l], 1});
for (int l = 0; l < v.size(); l++)
{
if (l != i)
{
q.push_back({v[l], 0});
}
}
sort(q.begin(), q.end(), cmp2);
vector<bool> pp;
for (int l = 0; l < q.size(); l++)
{
if (q[l].x == O)
continue;
pp.push_back(q[l].y);
}
// if (pp.size())
// pp.push_back(pp[0]);
for (int l = 0; l < pp.size() - 1; l++)
{
if (pp[l] && pp[l + 1])
ans++;
}
if(pp.size()>=2)
{
if(pp[pp.size()-1]&&pp[0])
ans++;
}
cout << ans << endl;
}
cout << ans + 1 << endl;
}
signed main()
{
ios;
int T = 1;
for (int i = 1; i <= T; i++)
{
// cout << "Case " << i << ": ";
solve();
}
return 0;
}
詳細信息
Test #1:
score: 0
Wrong Answer
time: 1ms
memory: 7744kb
input:
7 1 4 4 0 2 3 3 1 3 5 0 0 2 4
output:
3 6 9 10
result:
wrong answer 1st numbers differ - expected: '9', found: '3'