翻转二叉树

翻转一棵二叉树。
示例：

输入：

 4<br />   /   \<br />  2     7<br /> / \   / \<br />1   3 6   9<br />输出：
 4<br />   /   \<br />  7     2<br /> / \   / \<br />9   6 3   1

思路:把树和子树辨别出来,只要拥有叶,就可以当作一个子树,使用递归实现,将所有树的左叶和右叶取出互换引用地址,一直递归

  public TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return null;
        }
        TreeNode left = invertTree(root.left);
        TreeNode right = invertTree(root.right);
        root.left=right;
        root.right=left;
        return root;
    }

全代码:

class TreeNode {
     int val;
     TreeNode left;
     TreeNode right;
     TreeNode(int val) { this.val = val; }
     TreeNode(int val, TreeNode left, TreeNode right) {
          this.val = val;
          this.left = left;
          this.right = right;
     }
 }
class Solution {
    public static void main(String[] args) {
        //构建一个树
        TreeNode treeNode1 = new TreeNode(9);
        TreeNode treeNode2 = new TreeNode(6);
        TreeNode treeNode3 = new TreeNode(7,treeNode2,treeNode1);
        TreeNode treeNode4 = new TreeNode(1);
        TreeNode treeNode5 = new TreeNode(3);
        TreeNode treeNode6 = new TreeNode(2,treeNode4,treeNode5);
        TreeNode treeNode = new TreeNode(4,treeNode6,treeNode3);
        Solution solution = new Solution();
        solution.invertTree(treeNode);
    }
    public TreeNode invertTree(TreeNode root) {
        //树为空
        if (root == null) {
            return null;
        }
        //左叶递归
        TreeNode left = invertTree(root.left);
        //右叶递归
        TreeNode right = invertTree(root.right);
        //树左叶和右叶互换
        root.left=right;
         //树左叶和右叶互换
        root.right=left;
        //返回树
        return root;
    }
}