题目：给你一个后缀表达式，展开成二叉树，然后从深层向根的方向输出树上的字符。

分析：DS，递归，搜索。利用递归建树，然后bfs，逆序输出即可。

说明：目标550题！

#include <algorithm>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <cmath>

using namespace std;

char Str[10001];

typedef struct tnode
{
	char   V;
	tnode *L;
	tnode *R;
}tnode;
tnode Node[10001];
int   TreeSize,Now;

tnode* madetree()
{
	int id = TreeSize ++;
	Node[id].V = Str[-- Now];
	if (Node[id].V <= 'Z') {
		Node[id].R = madetree();
		Node[id].L = madetree();
	}
	return &Node[id];
}

tnode* Q[10001];
char output[10001];
void bfs(tnode *root)
{
	int move = 0,save = 0,count = 0;
	Q[save ++] = root;
	while (move < save) {
		tnode* now = Q[move ++];
		output[count ++] = now->V;
		if (now->L) Q[save ++] = now->L;
		if (now->R) Q[save ++] = now->R;
	}
	while (count)
		printf("%c",output[-- count]);
	printf("\n");
}

int main()
{
	int t;
	while (~scanf("%d",&t))
	while (t --) {
		scanf("%s",Str);
		TreeSize = 0;
		memset(Node, 0, sizeof(Node));
		Now = strlen(Str);
		bfs(madetree());
	}
    return 0;
}

UVa 11234 - Expressions