HDU

HDU3999 The order of a Tree

題目連結

  • 題意：給定一顆二叉樹，要以最小字典序印出這棵樹。
  • 題解：要以最小字典序印出這棵樹，就是以前序印訪問。所以先建立出二元樹，再 dfs 就可了。
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    #pragma GCC optimize("O2")
    #include <bits/stdc++.h>
    using namespace std;
    using LL = long long;
    using ULL = unsigned long long;
    using PII = pair<int, int>;
    using PLL = pair<LL, LL>;
    using VI = vector<int>;
    using VVI = vector<vector<int>>;
    const int INF = 1e9;
    const int MXN = 0;
    const int MXV = 0;
    const double EPS = 1e-9;
    const int MOD = 1e9 + 7;
    #define MP make_pair
    #define PB push_back
    #define F first
    #define S second
    #define FOR(i, L, R) for (int i = L; i < (int)R; ++i)
    #define FORD(i, L, R) for (int i = L; i > (int)R; --i)
    #define IOS                                                                    \
        cin.tie(nullptr);                                                          \
        cout.tie(nullptr);                                                         \
        ios_base::sync_with_stdio(false);
    struct Node
    {
        int val;
        Node *Lc, *Rc;
        Node() : Lc(nullptr), Rc(nullptr) {}
    };

    Node *insert(Node *node, int val)
    {
        if (node == nullptr)
        {
            node = new Node();
            node->val = val;
        }
        else if (val < node->val)
        {
            node->Lc = insert(node->Lc, val);
        }
        else
        {
            node->Rc = insert(node->Rc, val);
        }
        return node;
    }
    bool first;

    void dfs(Node *node)
    {
        if (node == nullptr)
        {
            return;
        }
        if (!first)
        {
            cout << ' ';
        }
        first = false;
        cout << node->val;
        dfs(node->Lc);
        dfs(node->Rc);
    }

    int main()
    {
        IOS;
        int n, x;
        while (cin >> n)
        {
            Node *root = nullptr;
            FOR(i, 0, n)
            {
                cin >> x;
                root = insert(root, x);
            }
            first = true;
            dfs(root);
            cout << '\n';
        }
    }

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