Depth First Search (DFS) Algorithm

import sys

sys.setrecursionlimit(10 ** 6)          # Increase the recursion limit so that DFS can execute correctly

n, e = map(int, input().split())        # n: vertices, e: edges
g = [[] for _ in range(n)]              # graph - adjacency list
used = [False] * n                      # used vertices (visited)

for _ in range(e):                      # read edges
    a, b = map(int, input().split())    # a -> b and b -> a
    g[a].append(b)
    g[b].append(a)


def dfs(v):                             # depth-first search
    used[v] = True                      # mark vertex as visited
    print(v, end=' ')                   # print vertex
    for to in g[v]:                     # for each vertex connected to v
        if not used[to]:                # if vertex is not visited
            dfs(to)                     # call dfs on that vertex


start = int(input())                    # start vertex
dfs(start)                              # call dfs on start vertex