1.根据二叉树创建字符串

题目链接：. - 力扣（LeetCode）

class Solution {
    public String tree2str(TreeNode root) {
        if(root==null){
            return null;
        }
        StringBuilder stringBuilder=new StringBuilder();
        tree2strChild(root,stringBuilder);
        return stringBuilder.toString();
    }
    public void tree2strChild(TreeNode t,StringBuilder stringBuilder){
        if(t==null){
            return;
        }
        stringBuilder.append(t.val);
        if(t.left!=null){
            stringBuilder.append("(");
            tree2strChild(t.left,stringBuilder);
            stringBuilder.append(")");
        }else{
            if(t.right==null){
                return;
            }else{
                stringBuilder.append("()");
            }
        }
        if(t.right!=null){
            stringBuilder.append("(");
             tree2strChild(t.right,stringBuilder);
            stringBuilder.append(")");
        }else{
            return;
        }
    }
}

2.二叉树前序非递归遍历实现

题目链接：. - 力扣（LeetCode）

public void preOrderTree(TreeNode root){
        Stack<TreeNode> stack=new Stack<>();
        if(root==null){
            return ;
        }
        TreeNode cur=root;
        while (cur!=null || !stack.isEmpty()){
            while (cur!=null){
                stack.push(cur);
                System.out.println(cur.val+" ");
                cur=cur.left;
            }
            TreeNode top=stack.pop();
            cur=cur.right;
        }
    }

3.二叉树中序非递归遍历实现

题目链接：. - 力扣（LeetCode）

public void inOrderTree(TreeNode root){
        Stack<TreeNode> stack=new Stack<>();
        if(root==null){
            return ;
        }
        TreeNode cur=root;
        while (cur!=null || !stack.isEmpty()){
            while (cur!=null){
                stack.push(cur);
                cur=cur.left;
            }
            TreeNode top=stack.pop();
            System.out.println(top.val+" ");
            cur=cur.right;
        }
    }

4.二叉树后序非递归遍历实现

题目链接：. - 力扣（LeetCode）

public void postOrderTree(TreeNode root){
        Stack<TreeNode> stack=new Stack<>();
        if(root==null){
            return ;
        }
        TreeNode cur=root;
        TreeNode prev=null;
        while (cur!=null || !stack.isEmpty()){
            while (cur!=null){
                stack.push(cur);
                cur=cur.left;
            }
            TreeNode top=stack.peek();
            if(top.right==null || top.right==prev){
                System.out.println(top.val+" ");
                stack.pop();
                prev=top;
            }else {
                top=top.right;
            }
        }
    }

希望能对大家有所帮助！！！！