树的层序遍历

需要的数据结构

vector<vector<int>> //用来存储结果
vector<int> //用来存储每一层节点值
queue<Node*> //一个节点的队列

计算方法

二叉树的层序遍历

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> result;
        queue<TreeNode*> que;
        if(root != NULL)   que.push(root);
        while(!que.empty()){
            // cout<<"here";
            int queSize = que.size();            
            vector<int> res;
            for(int i = 0;i < queSize ;i++){
                TreeNode* now = que.front();
                que.pop();
                res.push_back(now->val);
                if(now->left != NULL) que.push(now->left);
                if(now->right != NULL)    que.push(now->right);
            }
            result.push_back(res);
        }
        return result;
    }

};

N叉树的层序遍历

给定一个 N 叉树，返回其节点值的层序遍历。（即从左到右，逐层遍历）。
树的序列化输入是用层序遍历，每组子节点都由 null 值分隔（参见示例）。
示例1

输入：root = [1,null,3,2,4,null,5,6]
输出：[[1],[3,2,4],[5,6]]

/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> children;
    Node() {}
    Node(int _val) {
        val = _val;
    }
    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    vector<vector<int>> levelOrder(Node* root) {
        vector<vector<int>> result; 
        queue<Node*> que;
        if(root != NULL)    que.push(root);
        while( !que.empty()){
            int queSize = que.size();
            vector<int> res;
            for(int i = 0; i< queSize;i++){
                Node * nowNode = que.front();
                que.pop();
                res.push_back(nowNode->val);
                for(int j = 0;j<nowNode->children.size();j++)  
                    que.push(nowNode->children[j]);
            }
            result.push_back(res);
        }
        return result;
    }
};