项目github地址：bitcarmanlee easy-algorithm-interview-and-practice 欢迎大家star，留言，一起学习进步
反转二叉树是数据结构中一种经典的操作。如下图所以，反转二叉树就是交换所有节点的左右子树。
具体代码实现如下：
节点类
/** * Created by wanglei on 17/8/5. */ public class TreeNode { int val = 0; TreeNode left = null; TreeNode right = null; public TreeNode(int val) { this.val = val; } } import java.util.LinkedList; import java.util.List; /** * Created by wanglei on 17/8/5. */ public class Solution { private int[] array = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; private static List<TreeNode> nodeList = null; public void createTree() { nodeList = new LinkedList(); for(int index = 0; index < array.length; index++) { nodeList.add(new TreeNode(array[index])); } //最后一个父节点在数组中的索引 int lastParentIndex = array.length / 2 - 1; for(int parentInex = 0; parentInex < lastParentIndex; parentInex++) { nodeList.get(parentInex).left = nodeList.get(parentInex * 2 + 1); nodeList.get(parentInex).right = nodeList.get(parentInex * 2 + 2); } // 最后一个父节点:因为最后一个父节点可能没有右孩子，所以单独拿出来处理 // 左孩子 nodeList.get(lastParentIndex).left = nodeList.get(lastParentIndex * 2 + 1); // 右孩子 if(array.length % 2 == 1) { nodeList.get(lastParentIndex).right = nodeList.get(lastParentIndex * 2 + 2); } } // 层次遍历 public void levelTraverse(TreeNode root) { if(root == null) return; LinkedList<TreeNode> list = new LinkedList<>(); list.add(root); while(list.size() != 0) { TreeNode node = list.removeFirst(); System.out.print(node.val + " "); if(node.left != null) { list.add(node.left); } if(node.right != null) { list.add(node.right); } } System.out.println(); } public TreeNode invertTree(TreeNode root) { if(root == null) return null; TreeNode tmp = root.left; root.left = root.right; root.right = tmp; invertTree(root.left); invertTree(root.right); return root; } public static void main(String[] args) { Solution solution = new Solution(); solution.createTree(); solution.levelTraverse(nodeList.get(0)); TreeNode newRoot = solution.invertTree(nodeList.get(0)); solution.levelTraverse(newRoot); } }最后输出的结果为：
1 2 3 4 5 6 7 8 9 1 3 2 7 6 5 4 9 8