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
        if (root == nullptr) {
            return {};
        }
        vector<vector<int>> v;
        queue<TreeNode*> qu;
        qu.push(root);
        while (qu.empty() == false) {
            vector<int> vv;
            int size = qu.size();
            while (size--) {
                vv.push_back(qu.front()->val);
                if (qu.front()->left != nullptr) {
                    qu.push(qu.front()->left);
                }
                if (qu.front()->right != nullptr) {
                    qu.push(qu.front()->right);
                }
                qu.pop();
            }
            if (vv.empty() == false) {
                v.push_back(vv);
            }
        }
        return v;
    }
};