在c++中从二叉树中获取最小的三个数字

#include <iostream>
#include <queue>

using namespace std;

// 二叉树节点定义
struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};

// 最小堆比较函数
struct Compare {
    bool operator()(const int& a, const int& b) {
        return a > b;
    }
};

// 从二叉树中获取最小的三个数字
vector<int> getMinThreeNumbers(TreeNode* root) {
    vector<int> result;
    if (root == nullptr) {
        return result;
    }

    // 创建最小堆
    priority_queue<int, vector<int>, Compare> minHeap;

    // 遍历二叉树
    queue<TreeNode*> q;
    q.push(root);
    while (!q.empty()) {
        TreeNode* node = q.front();
        q.pop();

        // 将节点值插入最小堆
        minHeap.push(node->val);

        // 将左右子节点加入队列
        if (node->left != nullptr) {
            q.push(node->left);
        }
        if (node->right != nullptr) {
            q.push(node->right);
        }
    }

    // 获取最小的三个数字
    while (!minHeap.empty() && result.size() < 3) {
        result.push_back(minHeap.top());
        minHeap.pop();
    }

    return result;
}

int main() {
    // 构建二叉树
    TreeNode* root = new TreeNode(5);
    root->left = new TreeNode(3);
    root->right = new TreeNode(8);
    root->left->left = new TreeNode(2);
    root->left->right = new TreeNode(4);
    root->right->left = new TreeNode(7);
    root->right->right = new TreeNode(9);

    // 获取最小的三个数字
    vector<int> minThree = getMinThreeNumbers(root);

    // 输出结果
    cout << "最小的三个数字为：";
    for (int num : minThree) {
        cout << num << " ";
    }
    cout << endl;

    return 0;
}