111. Minimum Depth of Binary Tree

以下是建立在后序遍历基础上的非递归代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

static int wing=[]()
{
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();

class Solution 
{
public:
    int minDepth(TreeNode* root) 
    {
        if(root==NULL)
            return 0;
        stack<TreeNode*> s;
        TreeNode* p=root;
        TreeNode* r=NULL;
        int count=INT_MAX;
        while(p||!s.empty())
        {
            if(p)
            {
                s.push(p);
                p=p->left;
            }
            else
            {
                p=s.top();
                if(p->right&&p->right!=r)
                {
                    p=p->right;
                    s.push(p);
                    p=p->left;
                }
                else
                {
                    if(p->left==NULL&&p->right==NULL)
                    {
                        int k=s.size();
                        count=min(count,k);
                    }                    
                    s.pop();
                    r=p;
                    p=NULL;
                }
            }
        }
        return count;
    }
};

下面是递归代码：

class Solution 
{
public:
    int minDepth(TreeNode* root) 
    {
        if(root==NULL)
            return 0;
        if(root->left==NULL)
            return 1+minDepth(root->right);
        if(root->right==NULL)
            return 1+minDepth(root->left);
        return 1+min(minDepth(root->left),minDepth(root->right));  
    }
};