C++非递归遍历二叉树

 

C++非递归前序遍历

/**
 * struct TreeNode {
 *  int val;
 *  struct TreeNode *left;\images\20211111\392807_1636599059575\FE67E09E9BA5661A7AB9DF9638FB1FAC
 *  struct TreeNode *right;
 *  TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param root TreeNode类
     * @return int整型vector
     */
    vector<int> preorderTraversal(TreeNode* root) {
        // write code here
        vector<int> listVal;
        stack<TreeNode*> treeStack;
        if(root == NULL) return listVal;
        treeStack.push(root);
        while(!treeStack.empty()){
            TreeNode *p = treeStack.top();
            treeStack.pop();
            listVal.push_back(p->val);
            cout<<p->val<<endl;
            //因为入栈的原因所以要右孩子先出战
            if(p->right != NULL){
                treeStack.push(p->right);
            }
            if(p->left != NULL){
                treeStack.push(p->left);
            }    
        }
        return listVal;
    }
};

 

C++非递归中序遍历

/**
 * struct TreeNode {
 *  int val;
 *  struct TreeNode *left;
 *  struct TreeNode *right;
 *  TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param root TreeNode类
     * @return int整型vector
     */
    vector<int> inorderTraversal(TreeNode* root) {
        // write code here
        vector<int> listVal;
        stack<TreeNode*> treeStack;
        if(root == NULL) return listVal;
        treeStack.push(root);
        TreeNode *p = root;
        while(!treeStack.empty()){
            if(p->left == NULL){
                p = treeStack.top();
                //cout<<p->val<<endl;
                listVal.push_back(p->val);
                treeStack.pop();
                p = p->right;
　　　　　　　　　　//当右孩子为NULL寻找上一级的右孩子
                while(!treeStack.empty() && p == NULL){
                    p = treeStack.top();
                    //cout<<p->val<<endl;
                    listVal.push_back(p->val);
                    treeStack.pop();
                    p = p->right;
                }
                if(p != NULL)
                    treeStack.push(p);
                else
                    continue;
            }
            if(p->left != NULL){
                p = p->left;
                treeStack.push(p);
            }    
        }
        return listVal;
    }
};