P1712 [NOI2016] 区间

https://www.luogu.com.cn/record/87172981

Luogu/P1712/P1712.cpp

@@ -0,0 +1,113 @@
+#include <iostream>
+#include <algorithm>
+#include <limits>
+#include <utility>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e5 + 5;
+
+struct node {
+    int l, r, m, d;
+
+    node(int _l = 0, int _r = 0)
+        : l(_l), r(_r), m(0), d(0) {}
+} tr[N << 3];
+
+void pushup(int u) {
+    tr[u].m = std::max(tr[u << 1].m, tr[u << 1 | 1].m);
+}
+
+void pushdown(int u) {
+    if (!tr[u].d) return;
+
+    tr[u << 1].d += tr[u].d;
+    tr[u << 1 | 1].d += tr[u].d;
+
+    tr[u << 1].m += tr[u].d;
+    tr[u << 1 | 1].m += tr[u].d;
+
+    tr[u].d = 0;
+}
+
+void build(int u, int l, int r) {
+    tr[u] = node(l, r);
+
+    if (l == r) return;
+
+    int mid = l + r >> 1;
+    build(u << 1, l, mid);
+    build(u << 1 | 1, mid + 1, r);
+}
+
+void modify(int u, int l, int r, int v) {
+    if (l <= tr[u].l && tr[u].r <= r) {
+        tr[u].d += v;
+        tr[u].m += v;
+
+        return;
+    }
+
+    pushdown(u);
+
+    int mid = tr[u].l + tr[u].r >> 1;
+    if (l <= mid) modify(u << 1, l, r, v);
+    if (r > mid) modify(u << 1 | 1, l, r, v);
+
+    pushup(u);
+}
+
+int n, m, ans = std::numeric_limits<int>::max();
+std::pair<int, int> seg[N];
+std::vector<int> nums;
+
+int len(int p) {
+    return nums[seg[p].second - 1] - nums[seg[p].first - 1];
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int n, m;
+
+    cin >> n >> m;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> seg[i].first >> seg[i].second;
+
+        nums.emplace_back(seg[i].first);
+        nums.emplace_back(seg[i].second);
+    }
+
+    std::sort(seg + 1, seg + 1 + n, [&](const std::pair<int, int> &a, const std::pair<int, int> &b) {
+        return a.second - a.first < b.second - b.first;
+    });
+
+    std::sort(nums.begin(), nums.end());
+    nums.erase(std::unique(nums.begin(), nums.end()), nums.end());
+
+    for (int i = 1; i <= n; i++) {
+        seg[i].first = std::lower_bound(nums.begin(), nums.end(), seg[i].first) - nums.begin() + 1;
+        seg[i].second = std::lower_bound(nums.begin(), nums.end(), seg[i].second) - nums.begin() + 1;
+    }
+
+    build(1, 1, nums.size());
+
+    for (int i = 1, l = 1; i <= n; i++) {
+        modify(1, seg[i].first, seg[i].second, 1);
+
+        while (tr[1].m >= m) {
+            ans = std::min(ans, len(i) - len(l));
+            modify(1, seg[l].first, seg[l].second, -1);
+            l++;
+        }
+    }
+
+    cout << (ans == std::numeric_limits<int>::max() ? -1 : ans) << endl;
+
+    return 0;
+}