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| #include <bits/stdc++.h>
#pragma optimization_level 3
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization ("unroll-loops")
#define MAX_N 505
#define INF 987654321
#define ll long long
#define pll pair<ll, ll>
#define vpll vector<pll>
#define vall3 vector<array<ll,3>>
#define all5 array<ll,5>
#define vall5 vector<all5>
#define vll vector<ll>
#define vs vector<string>
#define usll unordered_set<ll>
#define vvs vector<vs>
#define vvll vector<vll>
#define all(a) begin(a), end(a)
#define X first
#define Y second
using namespace std;
ll n;
vpll p;
ll ccw(pll &a, pll &b, pll &c) {
ll res = a.X * b.Y + b.X * c.Y + c.X * a.Y;
res -= (a.X * c.Y + b.X * a.Y + c.X * b.Y);
return res;
}
bool cmp(pll& a, pll& b) {
ll c=ccw(p[0], a, b);
if(c) return c > 0;
if(a.Y == b.Y) return a.X < b.X;
return a.Y > b.Y;
}
vpll solve() {
sort(all(p));
sort(begin(p) + 1, end(p), cmp);
vpll st;
st.push_back(p[0]);
st.push_back(p[1]);
for(ll i = 2; i < p.size(); i++) {
while(st.size() >= 2) {
auto s = st.back(); st.pop_back();
auto f = st.back();
if(ccw(p[i],s,f) <= 0) {
st.push_back(s);
break;
}
}
st.push_back(p[i]);
}
return st;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.setf(ios::fixed);
cout.precision(6);
scanf("%lld",&n);
char yn;
for(ll i = 0, y, x; i < n; i++) {
scanf("%lld %lld %c",&x,&y,&yn);
if(yn == 'Y')
p.push_back({x,y});
}
auto hull = solve();
printf("%lld\n",hull.size());
for(auto& [x, y] : hull)
printf("%lld %lld\n",x,y);
return 0;
}
|
