LeetCode94二叉树的中序遍历

（1）普通递归

/**
 * 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:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int>ves;
        inorder(root,ves);
        return ves;
    }
    void inorder(TreeNode* node,vector<int>& ves)
    {
        if(node!=NULL)
        {
            inorder(node->left,ves);
            ves.push_back(node->val);
            inorder(node->right,ves);
        }
    }
};

（2）迭代法

/**
 * 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:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int>ves;
        if(root==NULL){
            return ves;
        }
       using Pair=pair<TreeNode*,int>;
        stack<Pair> st;
        st.push(Pair(root,0));
        TreeNode* p;
        while(!st.empty())
        {
            Pair ptemp=st.top();
            p=ptemp.first;
            st.pop();
            if(p!=NULL){
               if(p->right!=NULL){
                st.push(Pair(p->right,0));
               }
               st.push(Pair(NULL,p->val));
                if(p->left!=NULL)
                {
                  st.push(Pair(p->left,0));
                }
            }else{
                ves.push_back(ptemp.second);
            }
        }
        return ves;
    }
};