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73 lines (64 loc) · 2.21 KB
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package codeforces.tree_basics;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.StringTokenizer;
public final class A {
public static void main(String[] args) throws IOException {
final FastScanner fs = new FastScanner();
final int n = fs.nextInt();
final Map<Integer, List<Integer>> g = new HashMap<>();
for (int i = 1; i < n; i++) {
final int l = fs.nextInt() - 1;
final int r = fs.nextInt() - 1;
g.computeIfAbsent(l, v -> new ArrayList<>()).add(r);
g.computeIfAbsent(r, v -> new ArrayList<>()).add(l);
}
final int[] res = { 0 };
dfs(0, -1, res, g);
System.out.println(res[0] * 3);
}
private static int dfs(int curr, int par, int[] diameter, Map<Integer, List<Integer>> g) {
int maxDepth = 0;
for (int next : g.getOrDefault(curr, Collections.emptyList())) {
if (next == par) {
continue;
}
final int depth = dfs(next, curr, diameter, g);
diameter[0] = Math.max(diameter[0], depth + maxDepth);
maxDepth = Math.max(depth, maxDepth);
}
return maxDepth + 1;
}
static class FastScanner {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st = new StringTokenizer("");
String next() {
while (!st.hasMoreTokens()) {
try {
st = new StringTokenizer(br.readLine());
} catch (IOException e) {
//noinspection CallToPrintStackTrace
e.printStackTrace();
}
}
return st.nextToken();
}
int nextInt() {
return Integer.parseInt(next());
}
int[] readArray(int n) {
final int[] a = new int[n];
for (int i = 0; i < n; i++) { a[i] = nextInt(); }
return a;
}
long nextLong() {
return Long.parseLong(next());
}
}
}