Find Bottom Left Tree Value

Given a binary tree, find the leftmost value in the last row of the tree.

Example 1:

Input:

    2
   / \
  1   3

Output:
1

Example 2:

Note: You may assume the tree (i.e., the given root node) is not NULL.

Solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    int maxD = -1;
    int minH = 0;
    int val = -1;
    
    public int findBottomLeftValue(TreeNode root) {
        pre(root, 0, 0);
        return val;
    }
    
    private void pre(TreeNode root, int d, int h) {
        if (root == null) return;
        if (d > maxD || d == maxD && h < minH) {
            maxD = d;
            minH = h;
            val = root.val;
        }
        pre(root.left, d + 1, h - 1);
        pre(root.right, d + 1, h + 1);
    }
}