rt,$O(n^2)$算法都能过。

我的代码：

#include <algorithm>
#include <cstdio>
#include <iostream>

using namespace std;

const int kMaxN = 1e5 + 1;

struct E {
  int x, y;
} a[kMaxN];

int n, cnt;

bool C(int x) {
  for (int i = 1; i <= n; ++i) {
    if (i != x && a[x].y <= a[i].y) {
      if (a[x].x <= a[i].x && a[x].x - a[x].y >= a[i].x - a[i].y || a[x].x >= a[i].x && a[x].x + a[x].y <= a[i].x + a[i].y) {
        return 1;
      }
    }
  }
  return 0;
}

int main() {
  ios::sync_with_stdio(0);
  cout.tie(0), cin.tie(0);
//  freopen("mountains.in", "r", stdin);
//  freopen("mountains.out", "w", stdout);
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i].x >> a[i].y;
  }
  cnt = n;
  for (int i = 1; i <= n; ++i) {
    cnt -= C(i);
  }
  cout << cnt << endl;
  return 0;
}