题目
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:
- 5 -> 3
- 5 -> 2 -> 1
- -3 -> 11
解题思路
遍历二叉树所有节点（任何遍历方式）
对每个节点，计算他和子节点组成的路径的节点值的和是否等于目标值，如果是，则路径的值加1
代码
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
var ret int
func downTravel(t *TreeNode, sumNeed, sumGet int) {
if nil == t {
return
}
sumGet += t.Val
if sumGet == sumNeed {
ret++
}
downTravel(t.Left, sumNeed, sumGet)
downTravel(t.Right, sumNeed, sumGet)
}
func preOrderTravel(t *TreeNode, sum int) {
if nil == t {
return
}
downTravel(t, sum, 0)
preOrderTravel(t.Left, sum)
preOrderTravel(t.Right, sum)
}
func pathSum(root *TreeNode, sum int) int {
ret = 0
preOrderTravel(root, sum)
return ret
}
