5.4.1 Minimum Depth of Binary Tree

Notes:
	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: 1. Recursion. Pay attention to cases when the non-leaf node has only one child.
	2. Iteration + Queue. Contributed by SUN Mian(孙冕).
	*/
	/**
	* Definition for binary tree
	* struct TreeNode {
	* int val;
	* TreeNode *left;
	* TreeNode *right;
	* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
	* };
	*/

int BiTree::minDepth(BiNode*root)
{
if (!root)
return 0;
return 1 + min(minDepth(root->lchild), minDepth(root->rchild));


}