invertBinaryTree.java

package week1;

/***
 * Given the root of a binary tree, invert the tree, and return its root.
 * Input: root = [4,2,7,1,3,6,9]
 * Output: [4,7,2,9,6,3,1]
 */
public class invertBinaryTree {
    public static void main(String[] args) {
        TreeNode node = new TreeNode(4);
        node.left = new TreeNode(2);
        node.right = new TreeNode(7);

        node.left.left = new TreeNode(1);
        node.left.right = new TreeNode(3);

        node.right.left = new TreeNode(6);
        node.right.right = new TreeNode(9);

        TreeNode result = invertTree(node);


    }

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

        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;

        invertTree(root.left);
        invertTree(root.right);
        return root;
    }

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

        TreeNode() {
        }

        TreeNode(int val) {
            this.val = val;
        }

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

}