Question

我可以按顺序打印我的表达式树。但我需要能够在括号内打印它。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 << ")";
    }
}

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

：（

Answer 1

您需要区分叶节点和非叶节点。只有非叶子节点包含在parantheses中。

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

尝试颠倒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 << ")";
    }
}

或者甚至可能更好：

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isoperator被适当地定义以区分运算符和操作数。

打印表达式树

2 个答案: