UVa 11234 Expressions

/*
coder: ACboy
date: 2010-3-7
result: AC
description: UVa 11234 Expressions
*/

#include <iostream>
#include <string>
using namespace std;

struct tree
{
tree* rchild;
tree* lchild;
char op;
};

// 用于创建表达式树用的栈
tree * Stack[10000];
// 用于树的层次遍历用的队列
tree * Queue[10000];
int front;
int rear;
int top;

// 创建了一颗没有孩子节点的树
tree * CreatTree(char a) {
tree * pnode = new tree;
pnode->rchild = NULL;
pnode->lchild = NULL;
pnode->op = a;
return pnode;
}

// 由两颗树作为左右孩子创建一颗树
tree * CreatTree(char a, tree * pl, tree * pr) {
tree * pnode = new tree;
pnode->rchild = pr;
pnode->lchild = pl;
pnode->op = a;
return pnode;
}

// 树的层次遍历
void levelOrder(tree * pF, int n) {
char ans[10000];
int count = 0;
front = 0;
rear = -1;
// 在使用全局变量的时候最好先初始化
// 之前因为没有初始化而一直WA，后来
// 发现是没有初始化，前面的数据会影响当前的数据。
memset(Queue, 0, sizeof(Queue));
Queue[front++] = pF;

while (rear < front) {
tree * pnode = Queue[++rear];
if (pnode != NULL) {
if (pnode->lchild != NULL) {
Queue[front++] = pnode->lchild;
}
if (pnode->rchild != NULL) {
Queue[front++] = pnode->rchild;
}
// 结果保存在ans数组中
ans[count++] = pnode->op;
}
}

// 逆序输出数组ans便得到结果
for (int i = count - 1; i >= 0; i--) {
cout << ans[i];
}
cout << endl;
}

int main() {
int n;
#ifndef ONLINE_JUDGE
freopen("11234.txt", "r", stdin);
#endif
cin >> n;
while (n--)
{
string str;
cin >> str;
int i;
int len = str.size();
top = 0;
for (i = 0; i < len; i++)
{
if (islower(str[i])) {
tree * ptree = CreatTree(str[i]);
Stack[top++] = ptree;
} else {
tree * prtree = Stack[--top];
tree * pltree = Stack[--top];
tree * pF = CreatTree(str[i], pltree, prtree);
Stack[top++] = pF;
}
}
levelOrder(Stack[top - 1], len);
}
return 0;
}