【LeetCode热题100】【二叉树】二叉树的层序遍历

题目链接：102. 二叉树的层序遍历 - 力扣（LeetCode）

借助队列实现广度优先搜索，遍历节点把子树入队

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode *root) {
        if (root == nullptr)
            return {};
        vector<vector<int>> ans;
        queue<TreeNode *> level;
        level.push(root);
        while (!level.empty()) {
            int levelSize = level.size();
            vector<int> temp;
            while (levelSize--) {
                TreeNode *node = level.front();
                level.pop();
                temp.push_back(node->val);
                if (node->left)
                    level.push(node->left);
                if (node->right)
                    level.push(node->right);
            }
            ans.push_back(std::move(temp));
        }
        return ans;
    }
};