Exercise: Search for a Value

Your Task

Write a function has_value(root, target) that returns True if target exists anywhere in the binary tree, or False if it doesn't.

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Examples

#       1
#      / \
#     2   3
#    / \
#   4   5

root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.left.right = TreeNode(5)

print(has_value(root, 4))   # True
print(has_value(root, 3))   # True
print(has_value(root, 99))  # False

print(has_value(None, 5))   # False

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Approach

1. Base case: if root is None, the value is not here — return False
2. Match: if root.val == target, we found it — return True
3. Otherwise, search the left subtree, then the right subtree
4. Return True if it was found in either side

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Hints