update

.gitignore

@@ -1,3 +1,4 @@
 .*
 build
 !.gitignore
+*.json

P2661/main.cpp

@@ -2,26 +2,42 @@
 #include <iostream>
 #include <istream>
 #include <queue>
-#include<vector>
+#include <vector>
+#include <functional>
 
 using std::cin,std::cout;
 
 const int MAX_N {(int)2e5+5};
 int n;
 std::vector<int> next[MAX_N];
-int inDegree[MAX_N];
+int in_degree[MAX_N];
 bool vis[MAX_N];
 std::queue<int> q;
 int ans;
 int input;
 
+int dfs(const int start, const int now, int depth){
+    depth++;
+    vis[now] = true;
+    int max_depth{ depth };
+    for (int i : next[now]) {
+        if (i == start) {
+            max_depth = std::max(max_depth, depth);
+        }
+        else {
+            max_depth = std::max(dfs(start, i, depth), max_depth);
+        }
+    }
+    return max_depth;
+};
+
 int main(){
     std::iostream::sync_with_stdio(false),cin.tie(nullptr),cout.tie(nullptr);
 
     std::cin>>n;
     for(int i=1;i<=n;i++){
         cin>>input;
-        inDegree[input]++;
+        in_degree[input]++;
         next[i].push_back(input);
     }
     const auto push_vis = [](int n){
@@ -29,7 +45,7 @@ int main(){
         vis[n]=true;
     };
     for(int i=1;i<=n;i++){
-        if(inDegree[i]<=0){
+        if(in_degree[i]<=0){
             push_vis(i);
         }
     }
@@ -37,26 +53,16 @@ int main(){
         int front = q.front();
         q.pop();
         for(int i:next[front]){
-            if(--inDegree[i]<=0){
+            if(--in_degree[i]<=0){
                 push_vis(i);
             }
         }
         
     }
-    const auto dfs = [](){
     
-    };
     for(int i=1;i<=n;i++){
         if(vis[i])continue;
-        int loop_size {0};
-        int start {i};
-        int now {start};
-        do{
-            vis[now]=true;
-            now=next[now];
-            loop_size++;
-        }while(now!=start);
-        ans=std::max(ans,loop_size);
+        ans=std::max(ans,dfs(i,i,0));
     }
     cout<<ans<<"\n";
 }