树结构最大值查找递归逻辑存疑及递归查找空值需求

Hey Joe, I totally get where you're stuck with recursion and tree structures—those recursive loops can feel like chasing your own tail at first! Let's break this down step by step, starting with the max value problem since you mentioned working on a leaf function for that.

Recursion works by splitting a big problem into identical smaller problems until you hit a "base case" (a simple scenario you can solve directly). For trees, every node is either a leaf (no children, just a value) or has child nodes that form smaller subtrees.

Let's assume your tree nodes look something like this (adjust the structure to match your actual code):

class TreeNode:
    def __init__(self, value=None, children=None):
        self.value = value
        self.children = children or []  # Empty list if no children

Here's how to write the recursive max-finding function:

def find_tree_max(node):
    # Base case: we've reached a leaf node—return its value
    if not node.children:
        return node.value
    
    # Recursive step: get the max value from each child subtree
    child_maxes = [find_tree_max(child) for child in node.children]
    # Compare current node's value with the max of all child values
    return max(node.value, max(child_maxes))

Let's walk through the logic: #

• When we hit a leaf (no children), we just return its value—no more recursion needed.
• For non-leaf nodes, we recursively call find_tree_max on every child. Each call solves the same problem but for a smaller subtree.
• Once we have the max value from all child subtrees, we compare it to the current node's value and return the larger one.

This follows the same recursive pattern—we check each node, then dig into its children. The goal is to return True if any node (including leaves) has a null value, otherwise False.

Using the same TreeNode class, here's the function:

def has_null_in_tree(node):
    # Base case: current node's value is null—we found one!
    if node.value is None:
        return True
    
    # Recursive step: check every child subtree
    for child in node.children:
        if has_null_in_tree(child):
            return True  # If any child has a null, we can stop early
    
    # If we made it here, no nulls were found in this node or its descendants
    return False

Key tips for recursion with trees: #

• Always define a clear base case first—this is what stops the recursion from running forever.
• For each recursive call, make sure you're passing a smaller piece of the problem (a child subtree, not the whole tree).
• Don't overcomplicate it: each recursive call only needs to handle the current node and delegate the rest to itself.

内容的提问来源于stack exchange，提问作者Joe