POJ 2255 根据二叉树的前序和中序序列来重建二叉树

#include <iostream>
#include <string>
using namespace std;
struct TreeNode{
	char val;
	TreeNode *left,*right;
};
TreeNode * bulidTree(string pre,string in){
	TreeNode * root =NULL;
	if (pre.length() > 0)
	{
		root = new TreeNode;
		root->val = pre[0];
		int index = in.find(pre[0]);
		//关键要理解再先序和后序序列中找左右子树的先序和后序序列的方法，利用递归实现
		root->left = bulidTree(pre.substr(1,index),in.substr(0,index));
		root->right = bulidTree(pre.substr(index+1),in.substr(index+1));
	}
	return root;
}
void PostTraverse(TreeNode * root){
	if (root != NULL)
	{
		PostTraverse(root->left);
		PostTraverse(root->right);
		cout<<root->val;
	}
}
int main(){
	string prestr,instr;
	while(cin>>prestr>>instr){
		TreeNode * root =bulidTree(prestr,instr);
		PostTraverse(root);
		cout<<endl;
	}
	return 0;
}