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
,
5
/ \
4 8
/ / \
11 13 4
/ \ \
7 2 1
return true, as there exist a root-to-leaf path 5->4->11->2
which sum is 22.
题目:根结点到叶结点的每个结点的和是否存在一条路径等于给定的sum
,如果等于sum
返回True,如果不等于sum
返回False。
思路:遍历根结点到叶结点的每个结点的和即可。
Language : python
最先想到以下方法,该方法遍历所有可能,然后返回最终的遍历结果。思路简单,但是缺点也明显,就是有多余的遍历。该方法不是找到满足要求的路径,立刻就返回,而是需要遍历所有的路径之后,再返回最终结果。
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def hasPathSum(self, root, sum):
"""
:type root: TreeNode
:type sum: int
:rtype: bool
"""
if not root:
return False
if not root.left and not root.right and root.val == sum:
return True
sum -= root.val
return self.hasPathSum(root.left, sum) or self.hasPathSum(root.right, sum)
这种方法是基于上面算法的改进,找到满足要求的路径,立马返回结果,不再继续遍历,速度变快很多。
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def hasPathSum(self, root, sum):
"""
:type root: TreeNode
:type sum: int
:rtype: bool
"""
if not root:
return False
elif not root.left and not root.right and root.val == sum:
return True
for child in (root.left, root.right):
if child:
if self.hasPathSum(child, sum - root.val):
return True
return False
Language : cpp
对应上述方法的C++代码
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
bool hasPathSum(TreeNode* root, int sum) {
if (root == NULL) return false;
else if (root->val == sum && root->left == NULL && root->right == NULL) return true;
if (root->left && hasPathSum(root->left, sum - root->val)) return true;
if (root->right && hasPathSum(root->right, sum - root->val)) return true;
return false;
}
};
LeetCode题目汇总: https://github.com/Jack-Cherish/LeetCode