https://leetcode.com/problems/find-bottom-left-tree-value/

Leetcode: 513. Find Bottom Left Tree Value

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func findBottomLeftValue(root *TreeNode) int {
    
    var find func(node *TreeNode, depth int) (int, int)
    find = func(node *TreeNode, depth int) (int, int) {
        if node == nil {
            return -1, -1
        }
        // leaf
        if node.Left == nil && node.Right == nil {
            return node.Val, depth
        }
        // find answer left
        left, leftDepth := find(node.Left, depth+1)
        // find answer right
        right, rightDepth := find(node.Right, depth+1)
        // prefer left
        if leftDepth >= rightDepth {
            return left, leftDepth
        }
        return right, rightDepth
    }
    v, _ := find(root, 0)
    return v
}