P1030 [NOIP2001 普及组] 求先序排列，洛谷，C++

#include<bits/stdc++.h>
using namespace std;
typedef struct node* tree;
struct node{
	char data;
	tree left,right;
};
tree root;
string in,last;
int k;
void buildTree(int L,int R,tree &t){
	if(L>R) return;
	int flag=-1;
	for(int i=L;i<=R;i++){
		if(in[i]==last[k]){
			flag=i;
			break;	
		}
	} 
	t=new node;
	t->data=in[flag];
	t->left=NULL;
	t->right=NULL;
	k--;
	buildTree(flag+1,R,t->right);
	buildTree(L,flag-1,t->left);
}
void preOrder(tree t){
	if(t){
		cout<<t->data;
		preOrder(t->left);
		preOrder(t->right);
	}
}
int main(){
	cin>>in>>last;
	k=last.length()-1;
	buildTree(0,k,root);
	preOrder(root);
	return 0;
}