UVa 11234 Expressions

一道树的题目

#include <iostream>
#include<deque>
#include<algorithm>
#include<cstdio>
#include<stack>
#include<string>
#include<vector>
#include<map>
#include<sstream>
#include<cctype>
#include<queue>
using namespace std;

struct node
{
    char data;
    node*left;
    node*right;
};

node* build(string s)
{
    stack<node *>st;
    for(int i=0;i<s.size();i++){
        if(isupper(s[i])){
            node *right = st.top();st.pop();
            node *left  = st.top();st.pop();
            node *nod   = new node;
            nod->left=left;nod->right=right;
            nod->data =s[i];
            st.push(nod);
        }
        else{
            node* nod=new node;
            nod->left=0;nod->right=0;
            nod->data = s[i];
            st.push(nod);
        }
    }
    return st.top();
}

string get_ans(node* root)
{
    queue<node*>q;
    q.push(root);
    string ans;
    while(!q.empty())
    {
        node*cur=q.front();q.pop();
        ans+=cur->data;
        if(cur->left)q.push(cur->left);
        if(cur->right)q.push(cur->right);
    }
    reverse(ans.begin(),ans.end());
    return ans;
}

int main()
{
    int n;
    string s;
    cin>>n;
    while(n--)
    {
        string ans;
        cin>>s;
        node* root=build(s);
        cout<<get_ans(root)<<endl;
    }
    return 0;
}