From f1eb76cd9e966bdbc73b50917be76fb39829f707 Mon Sep 17 00:00:00 2001
From: hanyixuanten <105723997+hanyixuanten@users.noreply.github.com>
Date: Fri, 10 Jul 2026 19:49:31 +0800
Subject: [PATCH] new file:   P1668.cpp

---
 P1668.cpp | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 P1668.cpp

diff --git a/P1668.cpp b/P1668.cpp
new file mode 100644
index 0000000..bd17681
--- /dev/null
+++ b/P1668.cpp
@@ -0,0 +1,79 @@
+#include <bits/stdc++.h>
+using namespace std;
+struct no
+{
+    int l, r, s;
+    inline const bool operator<(const no b) const
+    {
+        return r < b.r;
+    }
+} cow[(int)2.5e4 + 1], seg[(int)4e6 + 5];
+void init(int now, int l, int r)
+{
+    seg[now].l = l;
+    seg[now].r = r;
+    seg[now].s = 0x7f7f7f7f;
+    if (l != r)
+    {
+        init(now * 2, l, (l + r) / 2);
+        init(now * 2 + 1, (l + r) / 2 + 1, r);
+    }
+    return;
+}
+int query(int now, int l, int r)
+{
+    if (seg[now].l > r || seg[now].r < l)
+        return 0x7f7f7f7f;
+    if (seg[now].l >= l && seg[now].r <= r)
+        return seg[now].s;
+    int mid = (seg[now].l + seg[now].r) / 2;
+    if (r <= mid)
+        return query(2 * now, l, r);
+    else if (l >= mid + 1)
+        return query(2 * now + 1, l, r);
+    else
+        return min(query(2 * now, l, r), query(2 * now + 1, l, r));
+}
+void edit(int now, int num, int location)
+{
+    if (seg[now].l == seg[now].r)
+    {
+        seg[now].s = num;
+        return;
+    }
+    seg[now].s = min(num, seg[now].s);
+    int mid = (seg[now].l + seg[now].r) / 2;
+    if (location <= mid)
+        edit(2 * now, num, location);
+    else
+        edit(2 * now + 1, num, location);
+    return;
+}
+// int f[(int)2.5e4 + 1]; // 到i最小代价
+int n, t;
+int main()
+{
+    // freopen("cleaning.in", "r", stdin);
+    // freopen("cleaning.out", "w", stdout);
+    scanf("%d %d", &n, &t);
+    for (int i = 1; i <= n; ++i)
+    {
+        scanf("%d %d", &cow[i].l, &cow[i].r);
+    }
+    sort(cow + 1, cow + n + 1);
+    init(1, 0, t);
+    edit(1, 0, 0);
+    // query(1, 1, 1);
+    for (int i = 1; i <= n; ++i)
+    {
+        // printf("%d\n", i);
+        int q = query(1, cow[i].l - 1, cow[i].r - 1);
+        if (q + 1 < query(1, cow[i].r, cow[i].r))
+            edit(1, q + 1, cow[i].r);
+    }
+    // for (int i = 0; i <= t; ++i)
+    //     printf("%d ", f[i]);
+    int ans = query(1, t, t);
+    printf("%d\n", (ans > n) ? -1 : ans);
+    return 0;
+}
\ No newline at end of file