diff --git a/Luogu/problem/P3870/P3870.cpp b/Luogu/problem/P3870/P3870.cpp
new file mode 100644
index 00000000..a93bdbbf
--- /dev/null
+++ b/Luogu/problem/P3870/P3870.cpp
@@ -0,0 +1,79 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+struct node {
+    int l, r, s, d;
+
+    node() {
+        l = r = s = d = 0;
+    }
+
+    node(int _l, int _r) {
+        l = _l;
+        r = _r;
+        s = d = 0;
+    }
+} tr[100005 << 2];
+int n, m, op, a, b;
+
+void pushup(int u) {
+    tr[u].s = tr[u << 1].s + tr[u << 1 | 1].s;
+}
+
+void pushdown(int u) {
+    if (!tr[u].d) return;
+    tr[u << 1].d = !tr[u << 1].d;
+    tr[u << 1 | 1].d = !tr[u << 1 | 1].d;
+    tr[u << 1].s = tr[u << 1].r - tr[u << 1].l + 1 - tr[u << 1].s;
+    tr[u << 1 | 1].s = tr[u << 1 | 1].r - tr[u << 1 | 1].l + 1 - tr[u << 1 | 1].s;
+    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);
+    pushup(u);
+}
+
+void modify(int u, int l, int r) {
+    if (l <= tr[u].l && tr[u].r <= r) {
+        tr[u].d = !tr[u].d;
+        tr[u].s = tr[u].r - tr[u].l + 1 - tr[u].s;
+        return;
+    }
+    int mid = tr[u].l + tr[u].r >> 1;
+    pushdown(u);
+    if (l <= mid) modify(u << 1, l, r);
+    if (r > mid) modify(u << 1 | 1, l, r);
+    pushup(u);
+}
+
+int query(int u, int l, int r) {
+    if (l <= tr[u].l && tr[u].r <= r) {
+        return tr[u].s;
+    }
+    int mid = tr[u].l + tr[u].r >> 1;
+    int s = 0;
+    pushdown(u);
+    if (l <= mid) s += query(u << 1, l, r);
+    if (r > mid) s += query(u << 1 | 1, l, r);
+    return s;
+}
+
+int main() {
+    cin >> n >> m;
+    build(1, 1, n);
+    for (int i = 0; i < m; i++) {
+        cin >> op >> a >> b;
+        if (op == 0) {
+            modify(1, a, b);
+        } else if (op == 1) {
+            cout << query(1, a, b) << endl;
+        }
+    }
+    return 0;
+}