Find Bottom Left Tree Value问题及解法

问题描述：

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

示例：

Input:    2   / \  1   3Output:1

Input:        1       / \      2   3     /   / \    4   5   6       /      7Output:7

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

问题分析：

转换以下就是求每一层的最左侧的结点，即层次遍历法，当然亦可以用根的先序遍历。

过程详见代码：

/** * 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 maxDepth = 0, res = 0;bl(root, 1, maxDepth, res);return res;}void bl(TreeNode* root,int depth,int& maxDepth,int& res){if (root == nullptr) return;if (depth > maxDepth){maxDepth = depth;res = root->val;}bl(root->left, depth + 1, maxDepth, res);bl(root->right, depth + 1, maxDepth, res);}};