LeetCode#513 Find Bottom Left Tree Value

[Description]

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

Example 1:

Input:

2
/ \
1   3

Output:
1

Example 2: 

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.

[My Answer]

/**
* 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) {
DFS(root, 1);
return ans;
}
private:
int ans = 0, height = 0;
void DFS(TreeNode* r, int h) {
if (height < h) {
ans = r->val;
height = h;
}
if (r->left) {
DFS(r->left, h+1);
}
if (r->right) {
DFS(r->right, h+1);
}
}
};