b967: 第 4 題 血緣關係

#include<bits/stdc++.h>

#define MAX 100001

using namespace std;

vector <int> F[MAX];

int md;

int DFS(int x) {

	int max1, max2, result;

	if (F[x].size() == 0) return 0;

	if (F[x].size() == 1) return DFS(F[x][0])+1;

	else {

		for (int i = 0; i<F[x].size(); i++) {

			result = DFS(F[x][i]) + 1;

			if (i == 0) max1 = result;

			else if (i == 1) {

				if (max1 >= result) max2 = result;

				else {

					max2 = max1;

					max1 = result;

				}

			} else {

				if (max1 <= result) {

					max2 = max1;

					max1 = result;

				}

				else if (max2 < result) max2 = result;

			}

		}

		md = max(md, max1 + max2);

            return max1;

	}

}

int main() {

	int a, b,root,rd,n;

	bool isChild[MAX];

	while (scanf("%d", &n) != EOF) {

		md = 0;

		for (int i = 0; i<n; i++) {

			F[i].clear();

			isChild[i] = false;

		}

		for (int i = 1; i<n; i++) {

			scanf("%d %d", &a, &b);

			F[a].push_back(b);

			isChild[b] = true;

		}

		for (int i = 0; i < n; i++) {

			if (!isChild[i]) {

				root = i;

				break;

			}

		}

		rd = DFS(root);

	    md = max(rd,md);

		printf("%d\n", md);

	}

}