用隊列表演出堆疊
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，原來堆疊跟隊列有一個有趣的關係，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();
}
}