题解 | #求二叉树的层序遍历#

/**
 * struct TreeNode {
 *  int val;
 *  struct TreeNode *left;
 *  struct TreeNode *right;
 *  TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
#include <queue>
#include <vector>
class Solution {
  public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param root TreeNode类
     * @return int整型vector<vector<>>
     */
    vector<vector<int> > levelOrder(TreeNode* root) {
        // write code here
        vector<vector<int>> res;
        if(!root) return res; 
        queue<TreeNode*> que;
        que.push(root);
        while (!que.empty()) {
            int s = que.size();
            vector<int> vec;
            for (int i = 0; i < s; i++) {
                TreeNode* tmp = que.front();
                if (tmp->left) que.push(tmp->left);
                if (tmp->right) que.push(tmp->right);
                vec.push_back(tmp->val);
                que.pop();
            }
            res.push_back(vec);
        }
        return res;
    }
};