UVa 839 天平

原题链接:https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=780

先建立二叉树，之后遍历。

 #include<iostream>
 using namespace std;

 struct Node
 {
     int W1, D1, W2, D2;
     Node *left;
     Node *right;
 };

 bool flag;

 Node* creatTree()
 {
     Node* root = new Node;
     cin >> root->W1 >> root->D1 >> root->W2 >> root->D2;
     if (root->W1 == )  root->left = creatTree();
     else                root->left = NULL;
     if (root->W2 == )    root->right = creatTree();
     else                root->right = NULL;
     return root;
 }

 int balance(Node* root)
 {
     if (flag == false)  return ;
     if (root->W1 == )   root->W1 = balance(root->left);
     if (root->W2 == )     root->W2 = balance(root->right);
     if (root->W1*root->D1 != root->W2*root->D2)  flag = false;
     return(root->W1 + root->W2);
 }

 void remove_tree(Node* u)
 {
     if (u == NULL)  return;
     remove_tree(u->left);
     remove_tree(u->right);
     delete u;
 }

 int main()
 {
     int t;
     cin >> t;
     while (t--)
     {
         Node* root = NULL;
         flag = true;
         root=creatTree();
         flag = true;
         balance(root);
         if (flag == true)  cout << "YES" << endl;
         else               cout << "NO" << endl;
         remove_tree(root);
         if (t != )   cout << endl;
     }
 }

刘汝佳的书上给出了一个引用传值的简单的方法

 #include<iostream>
 using namespace std;

 bool solve(int &W)
 {
     int W1, D1, W2, D2;
     bool b1 = true, b2 = true;
     cin >> W1 >> D1 >> W2 >> D2;
     if (!W1)  b1 = solve(W1);
     if (!W2)  b2 = solve(W2);
     W = W1 + W2;
     return b1&&b2 && (W1*D1 == W2*D2);
 }

 int main()
 {
     int T, W;
     cin >> T;
     while (T--)
     {
         if (solve(W))  cout << "YES" << endl;
         else cout << "NO" << endl;
         if (T)  cout << endl;
     }
     return ;
 }