P3420 [POI2005] SKA-Piggy Banks

https://www.luogu.com.cn/record/168548666

Luogu/P3420/P3420.cpp

@@ -0,0 +1,47 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e6 + 5;
+
+int n, fa[N], cnt;
+
+int find(int x) {
+    return x == fa[x] ? x : fa[x] = find(fa[x]);
+}
+
+void merge(int x, int y) {
+    x = find(x);
+    y = find(y);
+
+    if (x != y) {
+        fa[x] = y;
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        fa[i] = i;
+    }
+
+    for (int i = 1, x; i <= n; i++) {
+        cin >> x;
+
+        merge(i, x);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        if (fa[i] == i) cnt++;
+    }
+
+    cout << cnt << endl;
+
+    return 0;
+}