题解 | #求二叉树的层序遍历#

/**
 * struct TreeNode {
 *  int val;
 *  struct TreeNode *left;
 *  struct TreeNode *right;
 * };
 */

class Solution {
  public:
    /**
     *
     * @param root TreeNode类
     * @return int整型vector<vector<>>
     */
    void levelOrder_per(vector<vector<int>>& resultvalues,
                        queue<TreeNode*>& tempq) {
        queue<TreeNode*> newqueue;
        vector<int>tempin;
        while (!tempq.empty()) {
            TreeNode* temptreenode = tempq.front();
            tempq.pop();
            tempin.push_back(temptreenode->val);
            if (temptreenode->left)newqueue.push(temptreenode->left);
            if (temptreenode->right)newqueue.push(temptreenode->right);
            if (tempq.empty()) {
                resultvalues.push_back(tempin);
                tempin.clear();
                swap(tempq,
                     newqueue);//交换队列(把空队列转给newqueue,把newqueue交给tempq接续遍历)
            }
        }
    }
    vector<vector<int> > levelOrder(TreeNode* root) {
        vector<vector<int>> tempresult;
        queue<TreeNode*> tempq;
        tempq.push(root);
        if (root == nullptr)return tempresult;
        levelOrder_per(tempresult, tempq);
        return tempresult;
    }
};