树的中序遍历新思路

Posted 2022-05-19 Fire king

class Solution 
    class ColorNode 
        TreeNode node;
        String color;
        
        public ColorNode(TreeNode node,String color)
            this.node = node;
            this.color = color;
        
    
    public List<Integer> inorderTraversal(TreeNode root) 
        if(root == null) return new ArrayList<Integer>();
            
        List<Integer> res = new ArrayList<>();
        Stack<ColorNode> stack = new Stack<>();
        stack.push(new ColorNode(root,"white"));
        
        while(!stack.empty())
            ColorNode cn = stack.pop();
            
            if(cn.color.equals("white"))
                if(cn.node.right != null) stack.push(new ColorNode(cn.node.right,"white"));
                stack.push(new ColorNode(cn.node,"gray"));
                if(cn.node.left != null)stack.push(new ColorNode(cn.node.left,"white"));
            else
                res.add(cn.node.val);
            
        
        
        return res;