Problem: 2063C - Remove Exactly Two
Language: python

Solution 1 (runtime: 781 ms):
t = int(input())

for x in range(t):
    n = int(input())
    edges = []
    adj_list = []

    for y in range(n+1):
        adj_list.append([])

    for e in range(n-1):
        a,b = list(map(int, input().split(" ")))
        
        adj_list[a].append(b)
        adj_list[b].append(a)


    for i in range(2):
        cnt_max_edges = 0
        max_edges = []
        for node in range(1, n+1):
            if adj_list[node] != None:
                if len(adj_list[node]) > cnt_max_edges:
                    cnt_max_edges = len(adj_list[node])
                    max_edges = [node]
                elif len(adj_list[node]) == cnt_max_edges:
                    max_edges.append(node)


        if len(max_edges) <= 2 or i == 1:
            max_edges = [max_edges[0]]
        else:
            f = False
            for idx1 in range(0, len(max_edges)):
                if f: break
                for idx2 in range(idx1+1, len(max_edges)):
                    if not max_edges[idx2] in adj_list[max_edges[idx1]]:
                        max_edges = [max_edges[idx1], max_edges[idx2]]
                        f = True
                        break


        for most_edges_node in max_edges:
            for node in adj_list[most_edges_node]:
                adj_list[node].remove(most_edges_node)

            adj_list[most_edges_node] = None

        if len(max_edges) >= 2:
            break

    count_cc = 0
    connected = {}
    v = 1
    for node in range(1, n+1):
        if adj_list[node] != None and not node in connected:
            queue = [node]

            while len(queue) > 0:
                curr = queue.pop()
                connected[curr] = count_cc
                for adj_node in adj_list[curr]:
                    if not adj_node in connected:
                        queue.append(adj_node)
                        connected[adj_node] = count_cc

            count_cc += 1

    print(count_cc)

Solution 2 (runtime: 718 ms):
import sys, math, collections, bisect, heapq, functools, itertools
sys.setrecursionlimit(10 ** 5)
inp = sys.stdin.readline
MOD = 10 ** 9 + 7
INF = 10 ** 20
MX = 10 ** 5 + 10
orda = ord('a')
fmax = lambda x, y: (x if x > y else y)
fmin = lambda x, y: (x if x < y else y)

def solve():
    N = int(inp())
    degree = [0 for _ in range(N + 1)]
    adj = [[] for _ in range(N + 1)]

    for _ in range(N - 1):
        u, v = list(map(int, inp().split()))
        adj[u].append(v)
        adj[v].append(u)
        degree[u] += 1
        degree[v] += 1

    tmp = []

    for node in range(1, N + 1):
        tmp.append((degree[node], node))

    tmp.sort(reverse=True)
    mx = tmp[0][0]
    best = i = 0

    def get_mx_branch(a, d, node):
        a = a[:]
        d = d[:]
        current, current_mx = d[node], 0

        d[node] = 0
        for u in a[node]:
            d[u] -= 1

        for i in range(1, N + 1):
            current_mx = fmax(current_mx, d[i])

        return current + current_mx - 1

    while i < N and tmp[i][0] == mx:
        if i > 1: break
        best = fmax(best, get_mx_branch(adj, degree, tmp[i][1]))
        i += 1

    return best
    
def main():
    for _ in range(int(inp())):
        print(solve())

if __name__ == '__main__':
    main()