package q437

type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

func count(node *TreeNode, prefix []int, target int) int {
	if node == nil {
		return 0
	}
	if len(prefix) > 0 {
		prefix = append(prefix, node.Val+prefix[len(prefix)-1])
	} else {
		prefix = append(prefix, node.Val)
	}

	cnt := 0
	for i := range len(prefix) - 1 {
		if prefix[len(prefix)-1]-prefix[i] == target {
			cnt++
		}
	}
	if prefix[len(prefix)-1] == target {
		cnt++
	}

	return cnt + count(node.Left, prefix, target) + count(node.Right, prefix, target)
}

func pathSum(root *TreeNode, targetSum int) int {
	return count(root, nil, targetSum)
}

var _ = pathSum