【leetcode刷题】T138-找树左下角的值

示例 1:
输入:
    2
   / \
  1   3
输出:
1

示例 2:
输入:
        1
       / \
      2   3
     /   / \
    4   5   6
       /
      7

输出:
7

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def findBottomLeftValue(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        # 层次遍历，找最左边的值
        # 中序遍历，找最深一层最左边的节点

        self.val = root.val
        self.depth = 1
        self.helper(root, 1)
        return self.val

    def helper(self, node, depth):
        if not node:
            return
        self.helper(node.left, depth+1)
        if depth > self.depth:
            self.val = node.val
            self.depth = depth
        self.helper(node.right, depth+1)

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int findBottomLeftValue(TreeNode* root) {
        int val = root->val;
        int max_depth = 1;
        helper(root, 1, val, max_depth);
        return val;
    }

    void helper(TreeNode* node, int depth, int& val, int& max_depth){
        if(!node)
            return ;
        helper(node->left, depth+1, val, max_depth);
        if(depth > max_depth){
            max_depth = depth;
            val = node->val;
        }
        helper(node->right, depth+1, val, max_depth);
    }
};