《数据结构与算法分析》学习笔记（四）——树ADT

一、二叉树

1、定义

         二叉树是一棵树，其中每个节点都不能多于2个儿子。

2、实现

typedef struct TreeNode *PtrToNode;
typedef PtrToNode Tree;
typedef char ElementType;

struct TreeNode
{
    ElementType Element;
    Tree Left;
    Tree Right;
};

3、通过后序表达式构造一个表达式树

void bianli(Tree t)
{
    if (t)
    {
        bianli(t->Left);
        cout << t->Element << " ";
        bianli(t->Right);
    }
}

int main()
{

    char c;
    stack<Tree> treeStack;

    while (1)
    {
        cout << "Please enter a suffix expression!(the last must is ‘;‘)" << endl;
        cin >> c;
        if (c == ‘;‘)
        {
            break;
        }
        else
        {
            if (c == ‘+‘ || c == ‘-‘ || c == ‘*‘ || c == ‘/‘)
            {
                auto t2 = treeStack.top();
                treeStack.pop();
                auto t1 = treeStack.top();
                treeStack.pop();

                PtrToNode temp2 = new(struct TreeNode);

                temp2->Element = c;
                temp2->Left = t1;
                temp2->Right = t2;

                treeStack.push(temp2);

            }
            else
            {
                PtrToNode temp;
                temp = new(struct TreeNode);
                temp->Element = c;
                temp->Left = temp->Right = nullptr;
                treeStack.push(temp);
            }
        }
    }

    auto t = treeStack.top();
    bianli(t);

    return 0;
}