Fix mypy errors at even_tree algo (TheAlgorithms#4579)

Author: mhihasan

graphs/even_tree.py

@@ -16,12 +16,12 @@
 from collections import defaultdict
 
 
-def dfs(start):
+def dfs(start: int) -> int:
     """DFS traversal"""
     # pylint: disable=redefined-outer-name
     ret = 1
     visited[start] = True
-    for v in tree.get(start):
+    for v in tree[start]:
         if v not in visited:
             ret += dfs(v)
     if ret % 2 == 0:
@@ -48,8 +48,8 @@ def even_tree():
 if __name__ == "__main__":
     n, m = 10, 9
     tree = defaultdict(list)
-    visited = {}
-    cuts = []
+    visited: dict[int, bool] = {}
+    cuts: list[int] = []
     count = 0
     edges = [(2, 1), (3, 1), (4, 3), (5, 2), (6, 1), (7, 2), (8, 6), (9, 8), (10, 8)]
     for u, v in edges: