2
xyPzwIM
abcABdefgCDEF

wzyxIPM
gfCecbDdAaEBF

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<string>
#include<stack>
#include<algorithm>
using namespace std;
char post[10010];
struct tree
{
    char ch;
    tree* lchild;
    tree* rchild;
};
tree* newnode()
{
    tree* u = (tree*) new (tree);
    u->ch = ‘\0‘;
    u->lchild = u->rchild = NULL;
    return u;
}
void bfs(tree* root)
{
    char out[10010];
    tree* que[10010] = {NULL};
    int font, rear, k = 0;
    font = 0, rear = 1;
    que[font] = root;
    out[k++] = root->ch;
    while(font < rear)
    {
        tree* tmp;
        tree* next;
        tmp = que[font++];
        if (tmp->lchild != NULL)
        {
            next = tmp->lchild;
            que[rear++] = next;
            out[k++] = next->ch;
        }
        if (tmp->rchild != NULL)
        {
            next = tmp->rchild;
            que[rear++] = next;
            out[k++] = next->ch;
        }
    }
    for (int i = k - 1; i >= 0; i--)
        cout<<out[i];
}
int main ()
{
    int t, i, n;
    cin>>t;
    getchar();
    while(t--)
    {
        gets(post);
        n = strlen(post);
        tree* s[10010];
        int k = 0;
        for (i = 0; i < n; i++)
        {
            if (post[i] <= ‘Z‘) //碰到操作符，从栈中取出两个地址，分别作为左右孩子，然后将其根地址再次入栈
            {
                tree* u = newnode();
                u->ch = post[i];
                u->rchild = s[--k];
                u->lchild = s[--k];
                s[k++] = u;
            }
            else //碰到操作数，将地址其入栈
            {
                tree* u = newnode();
                u->ch = post[i];
                s[k++] = u;
            }
        }
        tree* root = s[--k]; //把树的根节点取出
        bfs(root); //进行层次遍历
        puts("");
        memset(post, 0, sizeof(post));
    }
    return 0;
}