二叉树的前序，中序，后序遍历（迭代）

最新推荐文章于 2025-03-07 10:59:35 发布

原创最新推荐文章于 2025-03-07 10:59:35 发布 · 190 阅读

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本文介绍了二叉树的三种遍历方式：前序、中序和后序遍历，并提供了详细的Java实现代码。每种遍历方法都使用了栈来辅助实现非递归过程。

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二叉树类

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}

前序：

public class Solution {
    public List<Integer> preorderTraversal1(TreeNode root) {
        List<Integer> list = new LinkedList<>();
        if (root == null) return list;
        Stack<TreeNode> stack = new Stack<>();
        stack.add(root);
        while (!stack.isEmpty()) {
            TreeNode current = stack.pop();
            list.add( current.val);
            if (current.right != null) {
                stack.push(current.right);
            }
            if (current.left != null) {
                stack.push(current.left);
            }

        }
        return list;
    }
}

中序：

public class Solution {
    public List<Integer> inorderTraversal1(TreeNode root) {
        List<Integer> list = new ArrayList<>();
        Stack<TreeNode> stack = new Stack<>();
        TreeNode current = root;
        while (current != null || !stack.isEmpty()) {
            while (current != null) {
                stack.push(current);
                current = current.left;
            }
            current = stack.pop();
            list.add(current.val);
            current = current.right;
        }
        return list;
    }
}

后序：

public class Solution {
    public List<Integer> postorderTraversal1(TreeNode root) {
        List<Integer> list = new LinkedList<>();
        if (root == null) return list;
        Stack<TreeNode> stack = new Stack<>();
        stack.add(root);
        while (!stack.isEmpty()) {
            TreeNode current = stack.pop();
            list.add(0, current.val);
            if (current.left != null) {
                stack.push(current.left);
            }
            if (current.right != null) {
                stack.push(current.right);
            }
        }
        return list;
    }
}