[20251215] BOJ / P4 / Tourists / 권혁준

Author: oncsr

khj20006/202512/15 BOJ P4 Tourists.md

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+```cpp
+#include <bits/stdc++.h>
+using namespace std;
+
+int N;
+vector<vector<int>> v(200001);
+int dep[200001]{};
+int par[200001][18]{}, dist[200001][18]{};
+
+void dfs(int n, int p, int d) {
+    dep[n] = d, par[n][0] = p;
+    for(int i:v[n]) if(i != p) {
+        dfs(i,n,d+1);
+        dist[i][0] = 1;
+    }
+}
+
+int main() {
+    cin.tie(0)->sync_with_stdio(0);
+    
+    cin>>N;
+    for(int i=1,a,b;i<N;i++){
+        cin>>a>>b;
+        v[a].push_back(b);
+        v[b].push_back(a);
+    }
+    
+    dfs(1,0,0);
+    for(int k=1;k<18;k++) for(int i=1;i<=N;i++) {
+        par[i][k] = par[par[i][k-1]][k-1];
+        dist[i][k] = dist[i][k-1] + dist[par[i][k-1]][k-1];
+    }
+    
+    long long ans = 0;
+    for(int i=1;i<=N;i++) for(int j=i*2;j<=N;j+=i) {
+        int a = i, b = j, diff = abs(dep[a] - dep[b]);
+        
+        for(int k=0;k<18;k++) if(diff & (1<<k)) {
+            if(dep[a] > dep[b]) swap(a,b);
+            ans += dist[b][k];
+            b = par[b][k];
+        }
+        
+        for(int k=17;k>=0;k--) if(par[a][k] != par[b][k]) {
+            ans += dist[a][k] + dist[b][k];
+            a = par[a][k];
+            b = par[b][k];
+        }
+        if(a != b) {
+            ans += 2;
+        }
+        ans++;
+    }
+    
+    cout<<ans;
+    
+}
+```