LeetCode513. 找树左下角的值

package leetCode;

import entity.TreeNode;

import java.util.HashMap;
import java.util.Map;

/**
 * 513. 找树左下角的值
 * 给定一个二叉树的 根节点 root，请找出该二叉树的 最底层 最左边 节点的值。
 * <p>
 * 假设二叉树中至少有一个节点。
 * <p>
 * 示例 1:
 * 输入: root = [2,1,3]
 * 输出: 1
 * <p>
 * 示例 2:
 * 输入: [1,2,3,4,null,5,6,null,null,7]
 * 输出: 7
 *
 * @author 
 * @date 2022-06-22 09:25:26
 */
public class LeetCode513 {
    public static void main(String[] args) {
        TreeNode root = new TreeNode(1, new TreeNode(2, new TreeNode(4), null), new TreeNode(3, new TreeNode(5), new TreeNode(6, new TreeNode(7), null)));
        System.out.println(findBottomLeftValue(root));
    }

    /**
     * 找树左下角的值
     *
     * @param root
     * @return
     */
    public static int findBottomLeftValue(TreeNode root) {
        TreeNode curr = root;
        Map<String, Integer> map = new HashMap<>(16);
        map.put("layer", 0);
        map.put("tar", null);
        getList(1, map, curr);

        return map.get("tar");
    }

    /**
     * 递归遍历每个节点，当当前层数大于记录的层数时，就记录第一个节点，最后得到的就是最底层的最左变的节点值
     *
     * @param currLayer 当前层数
     * @param map       记录之前的层数和目标值
     * @param curr
     */
    private static void getList(int currLayer, Map<String, Integer> map, TreeNode curr) {
        if (curr == null) {
            return;
        }
        if (currLayer > map.get("layer")) {
            System.out.println(curr.val);
            map.put("tar", curr.val);
            map.put("layer", currLayer);
        }
        getList(currLayer + 1, map, curr.left);
        getList(currLayer + 1, map, curr.right);


    }
}


package entity;

/**
 *
 * @author 
 * @date 2022-06-22 09:37:36
 */

public class TreeNode {
    public int val;
    public TreeNode left;
    public TreeNode right;

    TreeNode() {
    }

    public TreeNode(int val) {
        this.val = val;
    }

    public TreeNode(int val, TreeNode left, TreeNode right) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}