From 514ec114cee74fe5590219e6e4a15ba70c8f0fb9 Mon Sep 17 00:00:00 2001
From: oncsr <khj20006@naver.com>
Date: Sat, 15 Nov 2025 11:23:10 +0900
Subject: [PATCH] =?UTF-8?q?[20251115]=20BOJ=20/=20P2=20/=20=EC=A0=90?=
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---
 ...355\224\204 \354\240\220\355\224\204 2.md" | 87 +++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 "khj20006/202511/15 BOJ P2 \354\240\220\355\224\204 \354\240\220\355\224\204 2.md"

diff --git "a/khj20006/202511/15 BOJ P2 \354\240\220\355\224\204 \354\240\220\355\224\204 2.md" "b/khj20006/202511/15 BOJ P2 \354\240\220\355\224\204 \354\240\220\355\224\204 2.md"
new file mode 100644
index 00000000..be610167
--- /dev/null
+++ "b/khj20006/202511/15 BOJ P2 \354\240\220\355\224\204 \354\240\220\355\224\204 2.md"	
@@ -0,0 +1,87 @@
+```cpp
+#include <bits/stdc++.h>
+using namespace std;
+
+int N, S;
+vector<vector<int>> v(100001), r(100001), g(100001);
+stack<int> st;
+bitset<100001> vis;
+int f[100001]{}, c[100001]{}, dp[100001]{}, deg[100001]{};
+set<pair<int, int>> s;
+
+void dfs1(int n) {
+    for(int i:v[n]) if(!vis[i]) {
+        vis[i] = 1;
+        dfs1(i);
+    }
+    st.push(n);
+}
+
+void dfs2(int n, int k) {
+    f[n] = k;
+    c[k]++;
+    for(int i:r[n]) if(!vis[i]) {
+        vis[i] = 1;
+        dfs2(i,k);
+    }
+}
+
+void dfs3(int n) {
+    for(int i:g[n]) {
+        deg[i]++;
+        if(!vis[i]) {
+            vis[i] = 1;
+            dfs3(i);
+        }
+    }
+}
+
+int main() {
+    cin.tie(0)->sync_with_stdio(0);
+
+    cin>>N;
+    for(int i=1,a;i<=N;i++) {
+        cin>>a;
+        if(i-a>=1) v[i].push_back(i-a), r[i-a].push_back(i);
+        if(i+a<=N) v[i].push_back(i+a), r[i+a].push_back(i);
+    }
+    cin>>S;
+    for(int i=1;i<=N;i++) if(!vis[i]) {
+        vis[i] = 1;
+        dfs1(i);
+    }
+
+    vis.reset();
+    int num = 0;
+    while(!st.empty()) {
+        int n = st.top(); st.pop();
+        if(vis[n]) continue;
+        vis[n] = 1;
+        dfs2(n,++num);
+    }
+
+    for(int i=1;i<=N;i++) for(int j:v[i]) {
+        if(f[i] != f[j] && !s.count(make_pair(f[i], f[j]))) {
+            g[f[i]].push_back(f[j]);
+            s.emplace(f[i], f[j]);
+        }
+    }
+
+    vis.reset();
+    dfs3(f[S]);
+    queue<int> q;
+    q.push(f[S]);
+    dp[f[S]] = c[f[S]];
+    int ans = 0;
+    while(!q.empty()) {
+        int n = q.front(); q.pop();
+        ans = max(ans, dp[n]);
+        for(int i:g[n]) {
+            dp[i] = max(dp[i], dp[n] + c[i]);
+            if(!--deg[i]) q.push(i);
+        }
+    }
+    cout<<ans;
+
+}
+```