[剑指Offer] 18.二叉树的镜像

题目描述

操作给定的二叉树，将其变换为源二叉树的镜像。 

输入描述:

    	    8
    	   /  
    	  6   10
    	 /   / 
    	5  7 9 11
    	镜像二叉树
    	    8
    	   /  
    	  10   6
    	 /   / 
    	11 9 7  5

【思路1】递归，左右孩子交换再分别递归左右子树

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    void Mirror(TreeNode *pRoot) {
        if(pRoot == NULL) 
            return ;
        TreeNode *temp = pRoot->left;
        pRoot->left = pRoot->right;
        pRoot->right = temp;
        Mirror(pRoot->left);
        Mirror(pRoot->right);
    }
};

【思路2】非递归，栈实现

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    void Mirror(TreeNode *pRoot) {
        if(pRoot == NULL) 
            return ;
        stack<TreeNode*> StackNode;
        StackNode.push(pRoot);
        while(!StackNode.empty()){
            TreeNode* tree = StackNode.top();
            StackNode.pop();
            if(tree->left || tree->right){
                TreeNode* temp = tree->left;
                tree->left = tree->right;
                tree->right = temp;
            }
            if(tree->left)
                StackNode.push(tree->left);
            if(tree->right)
                StackNode.push(tree->right);
        }
    }
};