题目大意：
给你中序和先序遍历的序列，要你输出后序遍历的结果。
思路：根据中序和先序建树然后后序输出即可。
代码：


#include<iostream>
#include<string.h>
#include<cstring>
using namespace std;

const int maxn = 10000;
char pre[maxn];
char in[maxn];
char l[maxn];
char r[maxn];
char build(int l1, int r1, int l2, int r2) {
	if (l1 > r1 || l2 > r2)return 0;
	char root = pre[l1];
	int k;
	for (int i = 0; i < strlen(in); i++) {
		if (root == in[i]) {
			k = i;
			break;
		}
	}
	int p = k - l2;
	l[root - 'A'] = build(l1 + 1, l1 + p, l2, p - 1+ l2);
	r[root - 'A'] = build(l1 +p + 1, r1, p + 1+ l2, r2);
	return root;
}
void postorder(char root) {
	if (root == '\0')return;
	postorder(l[root - 'A']);
	postorder(r[root - 'A']);
	cout << root;
}
int main() {
	while (cin >> pre >> in) {
		int n = strlen(pre) - 1;
		build(0, n, 0, n);
		postorder(pre[0]);
		cout<<endl; 
	}
}