二叉树后序遍历

Posted 2022-12-14 Blocking The Sky

堆栈非递归实现

class Solution 
public:
    vector<int> result;
    vector<int> postorderTraversal(TreeNode* root) 
        stack<TreeNode*> s;
        TreeNode *p;
        p=NULL;
        while(root||!s.empty())
            if(root)
                s.push(root);
                root=root->left;
            
            else
                root=s.top();
                if(root->right&&root->right!=p)//左子树不为空且没有访问过
                    root=root->right;
                
                else
                    s.pop();
                    //visit(root)
                    result.push_back(root->val);
                    p=root;//p更新右子树的根结点
                    root=NULL;//表示右子树遍历结束
                
            
        
        return result;
    
;

递归实现

class Solution 
public:
    vector<int> result;
    vector<int> postorderTraversal(TreeNode* root) 
        if(root)
            postorderTraversal(root->left);
            postorderTraversal(root->right);
            //visit(root)
            result.push_back(root->val);
        
        return result;
    
;