(4.10) Check Subtree py

CrackingTheCodingInterview/ch04-TreesAndGraphs/checkSubtree.py

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+"""
+T1 and T2 are two very large binary trees, with T1 much bigger
+than T2 - create an algorithm to determine if T2 is a subtree
+of T1
+"""
+
+
+# Traverse t1 until find value equal to t2, then check match_trees
+def is_subtree(t1, t2):
+    if not t2:
+        return True
+
+    if not t1:
+        return False
+
+    if match_trees(t1, t2):
+        return True
+
+    return is_subtree(t1.left, t2) or \
+        is_subtree(t1.right, t2)
+
+
+# Check if trees match exactly
+def match_trees(t1, t2):
+    # Both subtrees empty
+    if not t1 and not t2:
+        return True
+
+    # One subtree empty
+    if not t1 or not t2:
+        return False
+
+    # Values don't match
+    if t1.value !== t2.value:
+        return False
+
+    # Check both sides
+    return match_trees(t1.left, t2.left) and \
+        match_trees(t1.right, t2.right)
+