Interview----将一棵二叉树转换成其镜像

题目:输入一颗二元查找树,将该树转换为它的镜像,

即在转换后的二元查找树中,左子树的结点都大于右子树的结点。

用递归和循环两种方法完成树的镜像转换。

例如输入:

8

/ \

6 10

/ \ / \

5 7 9 11

输出:

8

/ \

10 6

/ \ / \

11 9 7 5

分析：

1. 递归，类似与先序和后序遍历。

2. 迭代：可以采用先序，后序的迭代版本，或者采用层序遍历也可。

二叉树的遍历的非递归版本可参考
点击打开链接

// copyrigth @ L.J.SHOU Mar.09, 2014
// find the mirror of a binary tree
#include <iostream>
#include <stack>
#include <queue>
using namespace std;

struct TreeNode{
int val;
TreeNode *left, *right;
TreeNode(int x)
:val(x), left(NULL), right(NULL){}
};

// recursive version
TreeNode* Mirror(TreeNode *root)
{
if(root == NULL)
return NULL;

swap(root->left, root->right);
root->left = Mirror(root->left);
root->right = Mirror(root->right);

return root;
}

// iterative version 1
// pre-order traversal
TreeNode* MirrorIterative(TreeNode *root)
{
if(root == NULL) return NULL;

TreeNode *p = root;
stack<TreeNode*> s;
while(p || !s.empty())
{
while(p){
swap(p->left, p->right);
s.push(p);
p = p->left;
}
p = s.top(); s.pop();
p = p->right;
}
return root;
}

// iterative version 2
// level order traversal
TreeNode* MirrorLevelOrder(TreeNode *root)
{
if(root == NULL) return NULL;

TreeNode *node(NULL);
queue<TreeNode *> cur, next;
cur.push(root);

while(!cur.empty())
{
while(!cur.empty()){
node = cur.front(); cur.pop();
swap(node->left, node->right);
if(node->left)
next.push(node->left);
if(node->right)
next.push(node->right);
}
swap(cur, next);
}
return root;
}

TreeNode* Destroy(TreeNode *root)
{
if(root == NULL) return NULL;
root->left = Destroy(root->left);
root->right = Destroy(root->right);
delete root;
return NULL;
}

void InOrder(TreeNode *root)
{
stack<TreeNode*> s;

while(root || !s.empty()){
while(root){
s.push(root);
root = root->left;
}
root = s.top(); s.pop();
cout << root->val << " ";
root = root->right;
}
cout << endl;
}

int main(void)
{
TreeNode *root(NULL);

root = new TreeNode(8);
root->left = new TreeNode(6);
root->right = new TreeNode(10);
root->left->left = new TreeNode(5);
root->left->right = new TreeNode(7);
root->right->left = new TreeNode(9);
root->right->right = new TreeNode(11);

root = MirrorLevelOrder(root);
InOrder(root);

root = Destroy(root);
return 0;
}