力扣：513. 找树左下角的值

import java.util.Deque;
import java.util.LinkedList;


public class Solution {
    public static void main(String[] args) {
        Solution solution = new Solution();
        TreeNode treeNode = new TreeNode(2, new TreeNode(1), new TreeNode(3));
        System.out.println(solution.findBottomLeftValue(treeNode));
    }

    int n = 0;
    int res = 0;
    public int findBottomLeftValue(TreeNode root) {
        dfs(root, 0);
        return res;
    }

    
    private void dfs(TreeNode root, int height){
        if (root == null){
            return;
        }
        height++;
        dfs(root.left, height);
        dfs(root.right, height);
        if (height > n){
            n = height;
            res = root.val;
        }
    }

    
    private int findBottomLeftValue2(TreeNode root){
        int res = 0;
        Deque stack = new LinkedList<>();
        stack.offer(root);
        while (!stack.isEmpty()){
            TreeNode temp = stack.poll();
            if (temp.right != null){
                stack.offer(temp.right);
            }
            if (temp.left != null){
                stack.offer(temp.left);
            }
            res = temp.val;
        }
        return res;
    }
}

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;
      }
  }