经验首页 前端设计 程序设计 Java相关 移动开发 数据库/运维 软件/图像 大数据/云计算 其他经验
当前位置:技术经验 » 程序设计 » C++ » 查看文章
C++实现LeetCode(102.二叉树层序遍历)
来源:jb51  时间:2021/7/21 18:17:39  对本文有异议

[LeetCode] 102. Binary Tree Level Order Traversal 二叉树层序遍历

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},

    3
/ \
9  20
/  \
15   7

return its level order traversal as:

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

层序遍历二叉树是典型的广度优先搜索 BFS 的应用,但是这里稍微复杂一点的是,要把各个层的数分开,存到一个二维向量里面,大体思路还是基本相同的,建立一个 queue,然后先把根节点放进去,这时候找根节点的左右两个子节点,这时候去掉根节点,此时 queue 里的元素就是下一层的所有节点,用一个 for 循环遍历它们,然后存到一个一维向量里,遍历完之后再把这个一维向量存到二维向量里,以此类推,可以完成层序遍历,参见代码如下:

解法一:

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        if (!root) return {};
        vector<vector<int>> res;
        queue<TreeNode*> q{{root}};
        while (!q.empty()) {
            vector<int> oneLevel;
            for (int i = q.size(); i > 0; --i) {
                TreeNode *t = q.front(); q.pop();
                oneLevel.push_back(t->val);
                if (t->left) q.push(t->left);
                if (t->right) q.push(t->right);
            }
            res.push_back(oneLevel);
        }
        return res;
    }
};

下面来看递归的写法,核心就在于需要一个二维数组,和一个变量 level,关于 level 的作用可以参见博主的另一篇博客 Binary Tree Level Order Traversal II 中的讲解,参见代码如下:

解法二:

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> res;
        levelorder(root, 0, res);
        return res;
    }
    void levelorder(TreeNode* node, int level, vector<vector<int>>& res) {
        if (!node) return;
        if (res.size() == level) res.push_back({});
        res[level].push_back(node->val);
        if (node->left) levelorder(node->left, level + 1, res);
        if (node->right) levelorder(node->right, level + 1, res);
    }
};

Github 同步地址:

https://github.com/grandyang/leetcode/issues/102

类似题目:

Binary Tree Level Order Traversal II

Binary Tree Zigzag Level Order Traversal

Minimum Depth of Binary Tree

Binary Tree Vertical Order Traversal 

Average of Levels in Binary Tree

N-ary Tree Level Order Traversal

参考资料:

https://leetcode.com/problems/binary-tree-level-order-traversal/

https://leetcode.com/problems/binary-tree-level-order-traversal/discuss/33445/Java-Solution-using-DFS

https://leetcode.com/problems/binary-tree-level-order-traversal/discuss/33450/Java-solution-with-a-queue-used

https://leetcode.com/problems/binary-tree-level-order-traversal/discuss/114449/A-general-approach-to-level-order-traversal-questions-in-Java

到此这篇关于C++实现LeetCode(102.二叉树层序遍历)的文章就介绍到这了,更多相关C++实现二叉树层序遍历内容请搜索w3xue以前的文章或继续浏览下面的相关文章希望大家以后多多支持w3xue!

 友情链接: NPS