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
O(n^2):
/**
* Definition for a binary tree node.
* public class TreeNode {
* public var val: Int
* public var left: TreeNode?
* public var right: TreeNode?
* public init(_ val: Int) {
* self.val = val
* self.left = nil
* self.right = nil
* }
* }
*/
class Solution {
func pathSum(_ root: TreeNode?, _ sum: Int) -> Int {
var path : [Int] = [], result : Int = 0
solve(root, sum, &path, &result)
return result
}
func solve(_ node: TreeNode?, _ sum: Int, _ path: inout [Int], _ result: inout Int) {
guard let node = node else { return }
path.append(node.val)
var total = sum
for i in stride(from: path.count-1, through: 0, by: -1) {
total-=path[i]
if total == 0 {
result+=1
}
}
solve(node.left, sum, &path, &result)
solve(node.right, sum, &path, &result)
path.removeLast()
}
}