diff --git a/graph-valid-tree/Leo.py b/graph-valid-tree/Leo.py
new file mode 100644
index 000000000..817ff1715
--- /dev/null
+++ b/graph-valid-tree/Leo.py
@@ -0,0 +1,18 @@
+class Solution:
+    def validTree(self, n: int, edges: List[List[int]]) -> bool:
+        # filter false cases by definition of tree
+        if n - 1 != len(edges):
+            return False
+
+        nodes = set()
+
+        for i, edge in enumerate(edges):
+            nodes.add(edge[0])
+            nodes.add(edge[1])
+
+            if i + 1 > len(nodes) - 1:
+                return False
+
+        return True
+
+        ## TC: O(num(edges)), SC: P(num(nodes))
diff --git a/number-of-connected-components-in-an-undirected-graph/Leo.py b/number-of-connected-components-in-an-undirected-graph/Leo.py
new file mode 100644
index 000000000..c2161a226
--- /dev/null
+++ b/number-of-connected-components-in-an-undirected-graph/Leo.py
@@ -0,0 +1,26 @@
+class Solution:
+    def countComponents(self, n: int, edges: List[List[int]]) -> int:
+
+        graph = collections.defaultdict(list)
+
+        for x, y in edges:
+            graph[x].append(y)
+            graph[y].append(x)
+
+        def dfs(node, visited):
+            visited.add(node)
+            for neighbor in graph[node]:
+                if neighbor not in visited:
+                    dfs(neighbor, visited)
+
+        count = 0
+        visited = set()
+
+        for node in range(n):
+            if node not in visited:
+                dfs(node, visited)
+                count += 1
+
+        return count
+
+        ## TC && SC: O(num(edge) + num(node))