打印表达式树

Question

我能够按顺序打印我的表达式树。但我需要能够用括号按顺序打印它。例如 postorder 53+ 应该输出 (5+3)

我目前有：

void printTree(struct TreeNode *tree)
{
   if (tree != NULL)
    {
      if (isalpha(tree->info) || isdigit(tree->info))
        cout << "(";
      printTree( tree->left);
      cout<< tree->info;
      printTree(tree->right);
      if (isalpha(tree->info) || isdigit(tree->info))
        cout << ")";
    }
}

但这给了我不正确的输出。如果我输入后缀表达式 62/5+ 它会给我 (6)/(2)+(5)

:(

Answer 1

您需要区分叶节点和非叶节点。只有非叶节点才用括号括起来。

bool isLeaf(struct TreeNode* tree) {
    return tree->left == 0 && tree->right == 0;
}

void printTree(struct TreeNode* tree) {
    if (tree != NULL) { // this test could be omitted if the printed tree is not empty
        if (isLeaf(tree)) {
            cout << tree->info;
        }
        else {
            cout << "(";
            printTree(tree->left);
            cout << tree->info;
            printTree(tree->right);
            cout << ")";            
        }
    }
}

Answer 2

尝试反转决定是否应打印括号的 if 条件：

void printTree(struct TreeNode *tree)
{
    if (tree != NULL)
    {
        if (!(isalpha(tree->info) || isdigit(tree->info)))
            cout << "(";
        printTree( tree->left);
        cout<< tree->info;
        printTree(tree->right);
        if (!(isalpha(tree->info) || isdigit(tree->info)))
            cout << ")";
    }
}

或者可能更好：

void printTree(struct TreeNode *tree)
{
    if (tree != NULL)
    {
        if (isoperator(tree->info))
            cout << "(";
        printTree( tree->left);
        cout<< tree->info;
        printTree(tree->right);
        if (isoperator(tree->info))
            cout << ")";
    }
}

其中适当定义了 isoperator 以区分运算符和操作数。