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.

Solution:

/**
 * 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 minDepth(TreeNode* root) {
        if ( root == NULL ) return 0;
        if ( root->left == NULL and root->right == NULL ) return 1;
        if ( root->left == NULL ) return minDepth(root->right) + 1;
        if ( root->right == NULL ) return minDepth(root->left) + 1;
        return min(minDepth(root->left), minDepth(root->right) ) + 1;
    }
};

Notes
Compare to maximum depth, note the difference!