如果你也像我这么写（这个代码是不能 AC 的）：
```cpp
#include <bits/stdc++.h>
const signed bufsize=5e6;__inline__ __attribute((always_inline))char Getchar(){static char buf[bufsize],*p1=buf,*p2=buf;return(p1==p2&&(p2=(p1=buf)+fread(buf,1,bufsize,stdin),p1==p2)?-1:*p1++);}template<class T>__inline__ __attribute((always_inline))void fr(register T&x){register char c,f;x^=x,c^=c,f^=f;do c^45?0:f|=1;while(c=Getchar(),c<48||c>57);do x=(x<<1)+(x<<3)+(c^48);while(c=Getchar(),c>47&&c<58);f?--x^=-1:0;}
using namespace std; namespace lgh {void main();} signed main() {
// freopen("2.in", "r", stdin);
// freopen("2.out", "w", stdout);
return lgh::main(), 0;} namespace lgh {
const int Maxn = 1e5 + 5, INF = 0x3f3f3f3f;
int N;
struct Point {int x, y;} pt[Maxn];
int X[Maxn], Xtop;
int Y[Maxn], Ytop;
int hd[Maxn], tl[Maxn], top[Maxn];
struct Bit {
int sum[Maxn];
#define lowbit(x) ((x) & -(x))
void modify(int x, int k) {
while (x <= Xtop) {
sum[x] += k;
x += lowbit(x);
}
}
int query(int x) {
int res = 0;
while (x >= 1) {
res += sum[x];
x -= lowbit(x);
}
return res;
}
} bit;
void main() {
fr(N);
for (int i = 1; i <= N; ++i) {
fr(pt[i].x), fr(pt[i].y);
X[++Xtop] = pt[i].x, Y[++Ytop] = pt[i].y;
}
sort(pt + 1, pt + N + 1, [](const Point &a, const Point &b) {return a.y < b.y;});
sort(X + 1, X + Xtop + 1); Xtop = unique(X + 1, X + Xtop + 1) - (X + 1);
sort(Y + 1, Y + Ytop + 1); Ytop = unique(Y + 1, Y + Ytop + 1) - (Y + 1);
fill(hd, hd + N + 1, INF);
for (int i = 1; i <= N; ++i) {
pt[i].x = lower_bound(X + 1, X + Xtop + 1, pt[i].x) - X;
pt[i].y = lower_bound(Y + 1, Y + Ytop + 1, pt[i].y) - Y;
hd[pt[i].y] = min(hd[pt[i].y], pt[i].x);
tl[pt[i].y] = max(tl[pt[i].y], pt[i].x);
top[pt[i].x] = max(top[pt[i].x], pt[i].y);
}
int ans = 0;
for (int i = 1, now = 1; i <= Ytop; ++i) {
if (tl[i] - hd[i] < 2) continue;
for (; now <= N && pt[now].y < i; ++now) {
if (pt[now].y != top[pt[now].x]) {
if (bit.query(pt[now].x) - bit.query(pt[now].x - 1) == 0) bit.modify(pt[now].x, 1);
}
else {
if (bit.query(pt[now].x) - bit.query(pt[now].x - 1) == 1) bit.modify(pt[now].x, -1);
}
}
ans += bit.query(tl[i] - 1) - bit.query(hd[i]);
}
printf("%d", N + ans);
}
}
```
by liugh_ @ 2024-04-27 13:44:53