二叉树 -- 5.1.1 Binary Tree Level Order Traversal-1 -- 图解-优快云博客

本文介绍了一种使用双队列实现的二叉树层序遍历算法，通过不断交换当前队列和下一个队列，实现了从左到右、逐层遍历二叉树节点值的功能。

/**********************************************************************************************************
Given a binary tree, return the level order traversal of its nodes’ values. (ie, from le to right, level by
level).
For example: Given binary tree {3,9,20,#,#,15,7},
3
/ \
9 20
/ \
15 7
return its level order traversal as:
[
[3],
[9,20],
[15,7]
]
**********************************************************************************************************/

Class Solution{
public:
        vector<vector<int> > levelOrder(TreeNode * root){
            vector<vector<int>> result;
            if(root == nullptr){
                return result;
            }
            queue<TreeNode*> current, next;
            vector<int> level;
            current.push(root);
            while(!current.empty()){
                while(!current.empty()){
                    TreeNode * node = current.front();
                    current.pop();
                    level.push_back(node);
                    if(node->left != nullptr) next.push(node->left);
                    if(node->right != nullptr) next.push(node->right);
                }
                result.push_back(level->val);
                level.clear();
                swap(next,current);
            }
            return result;
        }
};