Trees & Recursion

Java Invert / Mirror Binary Tree

Invert a binary tree by recursively swapping left and right child pointers.

Java Source Code

Editable code sample with line numbers

Java

class TreeNode {
    int val;
    TreeNode left, right;
    TreeNode(int val) { this.val = val; }
}

public class Main {
    public static TreeNode invertTree(TreeNode root) {
        if (root == null) return null;

// Recursively invert subtrees
        TreeNode left = invertTree(root.left);
        TreeNode right = invertTree(root.right);

// Swap children
        root.left = right;
        root.right = left;

return root;
    }

public static void printInOrder(TreeNode node) {
        if (node == null) return;
        printInOrder(node.left);
        System.out.print(node.val + " ");
        printInOrder(node.right);
    }

public static void main(String[] args) {
        TreeNode root = new TreeNode(4);
        root.left = new TreeNode(2);
        root.right = new TreeNode(7);
        root.left.left = new TreeNode(1);
        root.left.right = new TreeNode(3);
        root.right.left = new TreeNode(6);
        root.right.right = new TreeNode(9);

System.out.print("Original In-Order: ");
        printInOrder(root);
        System.out.println();

invertTree(root);

System.out.print("Inverted In-Order: ");
        printInOrder(root);
        System.out.println();
    }
}

Expected Output

When this program is compiled and executed, the terminal outputs:

Original In-Order: 1 2 3 4 6 7 9 
Inverted In-Order: 9 7 6 4 3 2 1

How the Code Works

Tree inversion visits each node once and swaps its left and right child pointers. A post-order recursive traversal solves this problem in linear time.

Time Complexity

O(N)

Space Complexity

O(H) recursion stack where H is tree height

Key Takeaways & Best Practices

Recursive tree algorithms naturally reduce subproblems to root-left-right pointer adjustments.

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Runnable Code

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How the Code Works

Tree inversion visits each node once and swaps its left and right child pointers. A post-order recursive traversal solves this problem in linear time.

Time Complexity

O(N)

Space Complexity

O(H) recursion stack where H is tree height

Key Takeaways & Best Practices

Recursive tree algorithms naturally reduce subproblems to root-left-right pointer adjustments.

Java Invert / Mirror Binary Tree

Java Source Code

Expected Output

How the Code Works

Key Takeaways & Best Practices

Master Java with ZenCompiler

Related Java Examples

Java Binary Tree Level Order Traversal (BFS)

Java Two Sum Problem (Optimized One-Pass HashMap)

Java Program to Reverse a String (StringBuilder & Two Pointers)

Platform & Tools

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Company & Help

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Java Invert / Mirror Binary Tree

Java Source Code

Expected Output

How the Code Works

Key Takeaways & Best Practices

Master Java with ZenCompiler

Related Java Examples

Java Binary Tree Level Order Traversal (BFS)

Java Two Sum Problem (Optimized One-Pass HashMap)

Java Program to Reverse a String (StringBuilder & Two Pointers)