Binary Tree Level Order Traversal

最新推荐文章于 2022-02-20 23:20:19 发布

brucehb

最新推荐文章于 2022-02-20 23:20:19 发布

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本文详细介绍了如何使用队列实现二叉树的层次遍历，并通过具体例子展示了算法的应用。

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:
Given binary tree {3,9,20,#,#,15,7},

return its level order traversal as:

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

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int> > levelOrder(TreeNode *root) {
        vector<vector<int> > result;
        if (root == NULL)
        {
            return result;
        }
        
        queue<TreeNode*> buf;
        buf.push(root);
        buf.push(NULL);
        vector<int> cur;
        while (buf.size())
        {
            TreeNode *temp = buf.front();
            if (temp != NULL)
            {
                cur.push_back(temp->val);
                if (temp->left)
                {
                    buf.push(temp->left);
                }
                if (temp->right)
                {
                    buf.push(temp->right);
                }
            }
            else
            {
                result.push_back(cur);
                cur.clear();
                if (buf.size() == 1)
                {
                    break;
                }
                else
                {
                    buf.push(NULL);
                }
            }

            buf.pop();
        }

        return result;
    }
};