111. Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its minimum depth = 2.

#include <iostream>
#include <algorithm>

using namespace std;

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

int minDepth(TreeNode* root) {
   if(root == NULL) return 0;
   if(root->left && root->right)
       return min(minDepth(root->left), minDepth(root->right)) + 1;
   if(root->left || root->right)
       return max(minDepth(root->left), minDepth(root->right)) + 1;
   return 1;
}