513-Find Bottom Left Tree Value

Description

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

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Example 1:

Input:

    2
   / \
  1   3

Output:
1

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Example 2:

Input:

        1
       / \
      2   3
     /   / \
    4   5   6
       /
      7

Output:
7

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

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問題描述

給定二叉樹， 返回其最下層最左邊的節點的值

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問題分析

前序遍歷(先遍歷左子節點， 後遍歷右子節點), 遞迴的過程中注意利用當前節點的高度與當前最大高度

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解法1

class Solution {
    public int findBottomLeftValue(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList();
        queue.add(root);

        while (!queue.isEmpty()) {
            root = queue.poll();
            if (root.right != null) queue.add(root.right);
            if (root.left != null)  queue.add(root.left);
        }

        return root.val;
    }
}

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解法2

class Solution {
    private int val = 0;
    private int maxDepth = 0;

    public int findBottomLeftValue(TreeNode root) {
        find(root, 1);
        return val;
    }
    public void find(TreeNode root, int depth){
        if(root == null) return;
        if(depth > maxDepth){
            val = root.val;
            maxDepth = depth;
        }
        find(root.left, depth + 1);
        find(root.right, depth + 1);
    }
}