Initial commit

test99-3-4.cpp

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+// lanqiao182 小朋友崇拜圈
+#include<bits/stdc++.h>
+using namespace std;
+const int N = 1e5 + 10;
+int n, a[N], dfn[N], idx, mindfn;
+
+int dfs(int x){
+    dfn[x] = ++idx;
+    if(dfn[a[x]]){
+        if(dfn[a[x]] >= mindfn) return dfn[x] - dfn[a[x]] + 1;
+        return 0;
+    }
+    return dfs(a[x]);
+}
+
+int main(){
+    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
+    cin >> n;
+    for(int i = 1; i <= n; i++) cin >> a[i];
+    int ans = 0;
+    for(int i = 1; i <= n; i++){
+        if(!dfn[i]){
+            mindfn = idx + 1;
+            ans = max(ans, dfs(i));
+        }
+    }
+    cout << ans << endl;
+    return 0;
+}
+/* test samples 
+9
+3 4 2 5 3 8 4 6 9
+*/