思路：
线段树 + 离散化。
测试用例：
3 10
1 10
1 3
6 10
实现：
1 #include <bits/stdc++.h> 2 using namespace std; 3 typedef pair<int, int> pii; 4 const int N = 200005; 5 int tree[N << 2], lazy[N << 2], a[N]; 6 7 void init() 8 { 9 memset(tree, 0, sizeof tree); 10 memset(lazy, 0, sizeof lazy); 11 } 12 13 void pushdown(int num, int cl, int cr) 14 { 15 if (!lazy[num]) return; 16 tree[num << 1] = lazy[num] * cl; 17 tree[num << 1 | 1] = lazy[num] * cr; 18 lazy[num << 1] = lazy[num]; 19 lazy[num << 1 | 1] = lazy[num]; 20 lazy[num] = 0; 21 } 22 23 void update(int num, int l, int r, int x, int y, int p) 24 { 25 if (x <= l && y >= r) { tree[num] = (r - l + 1) * p; lazy[num] = p; return; } 26 int m = l + r >> 1; 27 pushdown(num, m - l + 1, r - m); 28 if (x <= m) update(num << 1, l, m, x, y, p); 29 if (y >= m + 1) update(num << 1 | 1, m + 1, r, x, y, p); 30 tree[num] = tree[num << 1] + tree[num << 1 | 1]; 31 } 32 33 int query(int num, int l, int r, int x, int y) 34 { 35 if (x <= l && y >= r) return tree[num]; 36 int m = l + r >> 1; 37 pushdown(num, m - l + 1, r - m); 38 int ans = 0; 39 if (x <= m) ans += query(num << 1, l, m, x, y); 40 if (y >= m + 1) ans += query(num << 1 | 1, m + 1, r, x, y); 41 return ans; 42 } 43 44 int main() 45 { 46 ios::sync_with_stdio(false); 47 init(); 48 int n, l, x, y; 49 cin >> n >> l; 50 vector<pii> q; 51 vector<int> v; 52 for (int i = 0; i < n; i++) 53 { 54 cin >> x >> y; 55 q.push_back(pii(x, y)); 56 v.push_back(x); v.push_back(y); 57 } 58 sort(v.begin(), v.end()); 59 v.erase(unique(v.begin(), v.end()), v.end()); 60 map<int, int> mp; 61 for (int i = 0; i < v.size(); i++) mp[v[i]] = 2 * i + 1; 62 int ans = 0, m = v.size() * 2; 63 for (int i = n - 1; i >= 0; i--) 64 { 65 int x = mp[q[i].first], y = mp[q[i].second]; 66 if (query(1, 1, m, x, y) < y - x + 1) ans++; 67 update(1, 1, m, x, y, 1); 68 } 69 cout << ans << endl; 70 return 0; 71 }