题目：

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.

题目解答：

这道题借助了之前做的层次遍历的题目的代码，增加了一个判断条件，如果可以确定当前节点是叶子节点，则返回其深度，也就是找到的最近的叶子节点的深度。

代码如下：

/**

 * 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) {

        int depth = 0;

        int curnum = 0;

        int childnum = 0;

        if(root == NULL)

        {

            return 0;

        }

        queue<TreeNode *> TreeQueue;

        TreeQueue.push(root);

        curnum = 1;

        while(curnum != 0)

        {

            vector<int> tmp;

            depth++;

            while(curnum != 0)

            {

                TreeNode *p = TreeQueue.front();

                tmp.push_back(p -> val);

                if((p -> left == NULL) && (p -> right == NULL))

                {

                    return depth;

                }

                if(p -> left != NULL)

                {

                    TreeQueue.push(p -> left);

                    childnum++;

                }

                if(p -> right != NULL)

                {

                    TreeQueue.push(p -> right);

                    childnum++;

                }

               

                TreeQueue.pop();

                curnum--;

            }

            curnum = childnum;

            childnum = 0;

        }

        return depth;

    }

};