leetcode_gym/_problems/pathSum3.md

layout, title, last_solved, category, leetcode_url, status

layout	title	last_solved	category	leetcode_url	status
page	Path Sum 3		tree	https://leetcode.com/problems/path-sum-iii/	Attempted

Problem

You are given a binary tree in which each node contains an integer value.

Find the number of paths that sum to a given value.

The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).

The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.

Example:

root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8

      10
     /  \
    5   -3
   / \    \
  3   2   11
 / \   \
3  -2   1

Return 3. The paths that sum to 8 are:

1.  5 -> 3
2.  5 -> 2 -> 1
3. -3 -> 11

Solution

This is a double nested dfs solution so runtime is horrible but it still works.

{% highlight python %}

def pathSum(self, root: TreeNode, sum: int) -> int:
    
    self.total = 0
    
    def helper(node, currSum):
        if not node:
            return
        
        helper(node.left, currSum+node.val)
        helper(node.right, currSum+node.val)
    
        if node.val + currSum == sum:
            self.total+=1
    
    
    def dfs(node):
        
        if not node: return
        
        helper(node, 0)
        
        dfs(node.left)
        dfs(node.right)
        
    
    dfs(root)
    
    return self.total

{% endhighlight %}

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{% highlight python %}

{% endhighlight %}