uva 11234

用queue表演出stack

很像是括號匹配的感覺，不過想破頭還是無法想出來

最後參考了網路上的解題報告，原來stack跟queue有一個有趣的關係，利用樹

//============================================================================
// Name        : Expressions.cpp
// Date : 2013/3/23 下午12:21:44
// Author : GCA
//============================================================================
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <climits>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <utility>
using namespace std;
#ifdef ONLINE_JUDGE
#define ll "%lld"
#else
#define ll "%I64d"
#endif
typedef unsigned int uint;
typedef long long int Int;
#define Set(a,s) memset(a,s,sizeof(a))
#define Write(w) freopen(w,"w",stdout)
#define Read(r) freopen(r,"r",stdin)
#define Pln() printf("\n")
#define I_de(x,n)for(int i=0;i<n;i++)printf("%d ",x[i]);Pln()
#define De(x)printf(#x"%d\n",x)
#define For(i,x)for(int i=0;i<x;i++)
#define CON(x,y) x##y
#define Pmz(dp,nx,ny)for(int hty=0;hty<ny;hty++){for(int htx=0;htx<nx;htx++){\
    printf("%d ",dp[htx][hty]);}Pln();}
#define M 30000
#define PII pair<int,int>
#define PB push_back
#define oo INT_MAX
#define Set_oo 0x3f
#define Is_debug true
#define debug(...) if(Is_debug)printf("DEBUG: "),printf(__VA_ARGS__)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define eps 1e-6
bool xdy(double x,double y){return x>y+eps;}
bool xddy(double x,double y){return x>y-eps;}
bool xcy(double x,double y){return x<y-eps;}
bool xcdy(double x,double y){return x<y+eps;}
int min3(int x,int y,int z){
    int tmp=min(x,y);
    return min(tmp,z);
}
int max3(int x,int y,int z){
    int tmp=max(x,y);
    return max(tmp,z);
}
struct node{
    int l,r;
    char w;
}tree[M];
int main() {
    ios_base::sync_with_stdio(0);
    int test;
    char str[M];
    scanf("%d",&test);
    while(test--){
        scanf("%s",str);
        int len=strlen(str);
        stack<int> st;
        for(int i=0;i<len;i++){
            if(isupper(str[i])){
                int r=st.top();
                st.pop();
                int l=st.top();
                st.pop();
                tree[i].w=str[i];
                tree[i].l=l;
                tree[i].r=r;
                st.push(i);

            }else{
                tree[i].w=str[i];
                tree[i].l=-1;
                tree[i].r=-1;
                st.push(i);
            }
        }

        int root=st.top();
        queue<int> q;
        vector<char> ans;
        q.push(root);
        while(!q.empty()){
            int tmp=q.front();q.pop();
//            debug("%d\n",tmp);
            ans.PB(tree[tmp].w);

            if(tree[tmp].l!=-1)
                q.push(tree[tmp].l);
            if(tree[tmp].r!=-1)
                q.push(tree[tmp].r);
        }
        for(int i=ans.size()-1;i>=0;i--){
            putchar(ans[i]);
        }Pln();
    }

}