边工作边刷题：70天一遍leetcode: day 16-1

Minimum Depth of Binary Tree

同理，这题用preorder iterative搞定。注意即使是preorder一个高度变量是不够的。因为在同一高度同时入栈左右，左边出栈后并不知道当前栈内的是右子树还是上一层。这样就没法用同一个变量track height了

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def minDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root: return 0
        stk = [(root, 1)]
        mh = sys.maxint
        while stk:
            cur = stk[-1][0]
            h = stk[-1][1]
            stk.pop()
            more = False
            if cur.right:
                stk.append((cur.right, h+1))
                more = True

            if cur.left:
                stk.append((cur.left, h+1))
                more = True

            if not more:
                if h<mh:
                    mh = h
        return mh