Minimum Depth of Binary Tree

Problem

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.

---

Idea

DFS 遍历树， 方法是用栈，压入root,1。 然后每次都先弹出然后压入其left和right。

---

Note

如何制作一个pair压入栈中

---

Solution

---