Path Sum Leetcode Python

最新推荐文章于 2020-04-27 23:05:45 发布

hyperbolechi

最新推荐文章于 2020-04-27 23:05:45 发布

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分类专栏： leetcode 文章标签： Tree leetcode python

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本文详细介绍了如何通过遍历整个二叉树来查找是否存在一条从根节点到叶子节点的路径，其路径上节点值之和等于给定的数值。该问题的时间复杂度为O(n)，其中n为二叉树的节点数量。

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Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

For example:

Given the below binary tree and sum = 22,

这题要求求出从root到leaf的和是否有等于sum的一条path.做法是遍历整个tree 满足条件则返回True 时间复杂度为O(n)

This problem can be solved by traverse the whole tree and find any path meet root to leaf sum equal to sum.

# Definition for a  binary tree node
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    # @param root, a tree node
    # @param sum, an integer
    # @return a boolean
    def hasPathSum(self, root, sum):
        if root==None:
            return False
        if root.val==sum and root.left==None and root.right==None:
            return True
        return self.hasPathSum(root.left,sum-root.val) or self.hasPathSum(root.right,sum-root.val)