剑指offer 二叉树镜像

题目描述

操作给定的二叉树，将其变换为源二叉树的镜像。
思路：前序遍历，把根的左右两个值交换，然后分别递归遍历左右子树。
/**
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;

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

}

}
*/
public class Solution {
public void Mirror(TreeNode root) {
if (root == null)
return;
if (root.left == null && root.right == null)
return;
TreeNode pTemp = root.left;
root.left = root.right;
root.right = pTemp;
if (root.left != null)
Mirror(root.left);
if (root.right != null)
Mirror(root.right);
}
}非递归： 用栈来实现
import java.util.Stack;

public class Solution {
public void Mirror(TreeNode root) {
if(root == null){
return;
}
Stack<TreeNode> stack = new Stack<TreeNode>();
stack.push(root);
while(!stack.isEmpty()){
TreeNode node = stack.pop();
if(node.left != null||node.right != null){
TreeNode temp = node.left;
node.left = node.right;
node.right = temp;
}
if(node.left!=null){
stack.push(node.left);
}
if(node.right!=null){
stack.push(node.right);
}
}
}
}