szjy_6_树_010

阅读代码，程序输出是（ ）。

#include <iostream>
using namespace std;

struct Node {
char value;
Node* left = nullptr;
Node* right = nullptr;
};

void walk(Node* root) {
if (root == nullptr) return;
walk(root->left);
walk(root->right);
cout << root->value;
}

int main() {
Node a{'A'}, b{'B'}, c{'C'}, d{'D'}, e{'E'}, f{'F'};
a.left = &b;  a.right = &c;
b.left = &d;  b.right = &e;
c.right = &f;
walk(&a);
}

{{ select(1) }}

• ABDECF
• DEBFCA
• DBEFCA
• DEBCFA