leetcode-513-Find-Bottom-Left-Tree-Value

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描述

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

Example 1:

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Input:

    2
   / \
  1   3

Output:
1

Example 2: 

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Input:

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

Output:
7

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

分析

其实就是求树的高度，深度优先遍历即可。

解决方案1(Java)

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private int value = 0;
    private int maxDepth = 0;
    public int findBottomLeftValue(TreeNode root) {
        dfs(root, 1);
        return value;
    }
    
    private void dfs(TreeNode root, int depth) {
        if (depth > maxDepth) {
            value = root.val;
            maxDepth = depth;
        }
        if (root.left != null) {
            dfs(root.left, depth + 1);
        }
        if (root.right != null) {
            dfs(root.right, depth + 1);
        }
    }
}

题目来源