513.cpp

// preorder.cpp
/**
 * 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 {
  int maxDepth = -1;
  int value;

public:
  int findBottomLeftValue(TreeNode *root) {
    value = root->val;
    preorder(root, 0);
    return value;
  }
  void preorder(TreeNode *root, int depth) {
    if (root == NULL)
      return;
    if (depth > maxDepth) {
      maxDepth = depth;
      value = root->val;
    }
    preorder(root->left, depth + 1);
    preorder(root->right, depth + 1);
  }
};