/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func findBottomLeftValue(root *TreeNode) int {
	if root == nil {
		return -1
	}
	queue := make([]*TreeNode, 0)
	queue = append(queue, root)
	for len(queue) != 0 {
		bl := queue[0].Val
		nextLV := make([]*TreeNode, 0)
		for len(queue) != 0 {
			head := queue[0]
			queue = queue[1:]
			if head.Left != nil {
				nextLV = append(nextLV, head.Left)
			}
			if head.Right != nil {
				nextLV = append(nextLV, head.Right)
			}
		}
		if len(nextLV) == 0 {
			return bl
		}
		queue = nextLV
	}
	return -1
}