English
112. Path Sum 
Problem Statement
Given the root of a binary tree and an integer targetSum, return true if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum.
A leaf is a node with no children.
Example 1:
Input: root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
Output: true
Explanation: The root-to-leaf path with the target sum is shown.
Example 2:
Input: root = [1,2,3], targetSum = 5
Output: false
Explanation: There two root-to-leaf paths in the tree:
(1 --> 2): The sum is 3.
(1 --> 3): The sum is 4.
There is no root-to-leaf path with sum = 5.
Example 3:
Input: root = [], targetSum = 0
Output: false
Explanation: Since the tree is empty, there are no root-to-leaf paths.
Constraints:
- The number of nodes in the tree is in the range
[0, 5000]. -1000 <= Node.val <= 1000-1000 <= targetSum <= 1000
Solution:
go
package main
// Definition for a binary tree node.
type TreeNode struct {
Val int
Left *TreeNode
Right *TreeNode
}
func hasPathSum(root *TreeNode, targetSum int) bool {
return dfs(root, targetSum, 0)
}
func dfs(node *TreeNode, targetSum int, sum int) bool {
if node == nil {
return false
}
sum += node.Val
if node.Left == nil && node.Right == nil {
return sum == targetSum
}
return dfs(node.Left, targetSum, sum) || dfs(node.Right, targetSum, sum)
}
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