P3875 [TJOI2010]被污染的河流

https://www.luogu.com.cn/record/86620351

Luogu/P3875/P3875.cpp

@@ -0,0 +1,121 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n, k;
+long long ans;
+std::vector<int> ys;
+
+struct Segment {
+    int x, y1, y2, k;
+
+    Segment()
+        : x(0), y1(0), y2(0), k(0) {}
+
+    Segment(int _x, int _y1, int _y2, int _k)
+        : x(_x), y1(_y1), y2(_y2), k(_k) {}
+
+    bool operator<(const Segment& b) const {
+        return x < b.x;
+    }
+};
+
+struct node {
+    int l, r;
+    long long cnt, len;
+
+    node(const int& _l = 0, const int& _r = 0)
+        : l(_l), r(_r), cnt(0), len(0) {}
+} tr[N << 2];
+
+inline int find(int y) {
+    return std::lower_bound(ys.begin(), ys.end(), y) - ys.begin();
+}
+
+inline void pushup(int u) {
+    if (tr[u].cnt) {
+        tr[u].len = ys[tr[u].r + 1] - ys[tr[u].l];
+    } else if (tr[u].l != tr[u].r) {
+        tr[u].len = tr[u << 1].len + tr[u << 1 | 1].len;
+    } else {
+        tr[u].len = 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 x) {
+    if (l <= tr[u].l && tr[u].r <= r) {
+        tr[u].cnt += x;
+    } else {
+        int mid = tr[u].l + tr[u].r >> 1;
+        if (l <= mid) modify(u << 1, l, r, x);
+        if (r > mid) modify(u << 1 | 1, l, r, x);
+    }
+
+    pushup(u);
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    std::vector<Segment> seg;
+
+    for (int i = 0; i < n; i++) {
+        int x1, y1, x2, y2;
+
+        cin >> x1 >> y1 >> x2 >> y2;
+
+        if (x1 == x2) {
+            if (y1 > y2) std::swap(y1, y2);
+
+            x1--, x2++;
+        } else if (y1 == y2) {
+            if (x1 > x2) std::swap(x1, x2);
+
+            y1--, y2++;
+        }
+
+        seg.emplace_back(x1, y1, y2, 1);
+        seg.emplace_back(x2, y1, y2, -1);
+
+        ys.push_back(y1);
+        ys.push_back(y2);
+    }
+
+    std::sort(ys.begin(), ys.end());
+    ys.erase(std::unique(ys.begin(), ys.end()), ys.end());
+
+    build(1, 0, ys.size() - 2);
+    std::sort(seg.begin(), seg.end());
+
+    for (int i = 0; i < seg.size(); i++) {
+        if (i > 0) {
+            ans += tr[1].len * (seg[i].x - seg[i - 1].x);
+        }
+
+        modify(1, find(seg[i].y1), find(seg[i].y2) - 1, seg[i].k);
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}