uva-11234-表达式

后缀表达式,使用队列计算,要求计算的结果一样,输出队列的输入串

表达式转二叉树,层次序遍历,先右孩子,然后字符串反转输出

#include <iostream>
#include <sstream>
#include<algorithm>
#include<memory.h>
#include<stdio.h>
#include<queue>
#include<stack>
using namespace std;
#define null NULL
const int N = 10000;

struct Node
{
    Node* p;
    Node* r;
    Node* l;
    char key;

    Node()
    {
        p = null;
        r = null;
        l = null;
        key = ‘0‘;
    }

};

void print(queue<Node*> q, string& str)
{
    Node* node = null;
    while (!q.empty())
    {
        node = q.front();
        q.pop();
        str += node->key;
        if (node->r != null)
            q.push(node->r);
        if (node->l != null)
            q.push(node->l);
    }
}

int main()
{
    freopen("d:\\1.txt", "r", stdin);
    int t;
    cin >> t;
    while (t--)
    {
        Node* root;
        string str;
        cin >> str;
        stack<Node*> s;
        int l = str.length();
        for (int i = 0; i < l; i++)
        {
            char c = str.at(i);
            Node* node = new Node();
            node->key = c;
            if (‘A‘ <= c && c <= ‘Z‘)
            {
                Node* l = s.top();
                s.pop();
                Node* r = s.top();
                s.pop();
                node->l = l;
                node->r = r;
            }
            s.push(node);
        }
        root = s.top();
        s.pop();
        queue<Node*> q;
        q.push(root);
        string& str1 = str;
        str="";
        print(q, str1);
        reverse(str.begin(), str.end());
        cout << str << endl;
    }
    return 0;
}