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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0501_0600.s0513_find_bottom_left_tree_value;

// #Medium #Depth_First_Search #Breadth_First_Search #Tree #Binary_Tree
// #2022_07_25_Time_0_ms_(100.00%)_Space_44.4_MB_(21.11%)

import com_github_leetcode.TreeNode;

/*
 * 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;
 *     }
 * }
 */
/**
 * 513 - Find Bottom Left Tree Value\.
 *
 * Medium
 *
 * Given the `root` of a binary tree, return the leftmost value in the last row of the tree.
 *
 * **Example 1:**
 *
 * ![](https://assets.leetcode.com/uploads/2020/12/14/tree1.jpg)
 *
 * **Input:** root = [2,1,3]
 *
 * **Output:** 1
 *
 * **Example 2:**
 *
 * ![](https://assets.leetcode.com/uploads/2020/12/14/tree2.jpg)
 *
 * **Input:** root = [1,2,3,4,null,5,6,null,null,7]
 *
 * **Output:** 7
 *
 * **Constraints:**
 *
 * *   The number of nodes in the tree is in the range [1, 10⁴].
 * *   -2³¹ <= Node.val <= 2³¹ - 1
**/
public class Solution {
    private int[] func(TreeNode root, int level) {
        if (root.left == null && root.right == null) {
            int[] a = new int[2];
            a[0] = root.val;
            a[1] = level;
            return a;
        }
        int[] a = null;
        int[] b = null;
        if (root.left != null) {
            a = func(root.left, level + 1);
        }
        if (root.right != null) {
            b = func(root.right, level + 1);
        }
        if (a == null) {
            return b;
        } else if (b == null) {
            return a;
        } else {
            if (a[1] >= b[1]) {
                return a;
            } else {
                return b;
            }
        }
    }

    public int findBottomLeftValue(TreeNode root) {
        int[] a = func(root, 0);
        if (a != null && a.length > 0) {
            return a[0];
        }
        return -1;
    }
}