LeetCode-Solutions-in-Cpp17

Solutions to high-frequency interview questions of LeetCode in C++17, taking into account both efficiency and comprehensibility.

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• 将节点存储到队列中，每次循环弹出一层，同时把下一层添加到队列中，队列为空则层次遍历结束

class Solution {
 public:
  vector<vector<int>> levelOrder(TreeNode* root) {
    vector<vector<int>> res;
    if (!root) {
      return res;
    }
    queue<TreeNode*> q;
    q.emplace(root);
    while (!empty(q)) {
      vector<int> line;
      int n = size(q);
      while (n--) {
        TreeNode* t = q.front();
        q.pop();
        line.emplace_back(t->val);
        if (t->left) {
          q.emplace(t->left);
        }
        if (t->right) {
          q.emplace(t->right);
        }
      }
      res.emplace_back(line);
    }
    return res;
  }
};