LintCode 69. 二叉树的层次遍历

Posted 2020-10-22 zslhg903

题目：给出一棵二叉树，返回其节点值的层次遍历（逐层从左往右访问）

 

样例

给一棵二叉树 {3,9,20,#,#,15,7} ：

  3
 / 9  20
  /   15   7

返回他的分层遍历结果：

[
  [3],
  [9,20],
  [15,7]
]

挑战 

挑战1：只使用一个队列去实现它

挑战2：用DFS算法来做

 

 

解：用队列

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */


class Solution {
public:
    /*
     * @param root: A Tree
     * @return: Level order a list of lists of integer
     */
    vector<vector<int>> levelOrder(TreeNode * root) {
        vector<vector<int>> res;
        if(root==NULL) return res;
        
        queue<TreeNode*> q;
        q.push(root);
        int sz;
        while(!q.empty())
        {
            vector<int> temp;
            sz=q.size();
            while(sz--)
            {
                TreeNode *fNode=q.front();
                temp.push_back(fNode->val);
                q.pop();
                if(fNode->left!=NULL)
                {
                    q.push(fNode->left);
                }
                if(fNode->right!=NULL)
                {
                    q.push(fNode->right);
                }
            }
            res.push_back(temp);
        }
        return res;
    }
};