|
| 1 | + |
| 2 | +>仰望星空的人,不应该被嘲笑 |
| 3 | + |
| 4 | +## 题目描述 |
| 5 | +给定一个二叉树,返回它的 前序 遍历。 |
| 6 | + |
| 7 | + 示例: |
| 8 | + |
| 9 | +```javascript |
| 10 | +输入: [1,null,2,3] |
| 11 | + 1 |
| 12 | + \ |
| 13 | + 2 |
| 14 | + / |
| 15 | + 3 |
| 16 | + |
| 17 | +输出: [1,2,3] |
| 18 | +``` |
| 19 | + |
| 20 | +进阶: 递归算法很简单,你可以通过迭代算法完成吗? |
| 21 | + |
| 22 | +来源:力扣(LeetCode) |
| 23 | +链接:https://leetcode-cn.com/problems/binary-tree-preorder-traversal |
| 24 | +著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。 |
| 25 | + |
| 26 | + |
| 27 | + |
| 28 | + |
| 29 | +## 解题思路 |
| 30 | + |
| 31 | +**递归解法** |
| 32 | + |
| 33 | +```javascript |
| 34 | +/** |
| 35 | + * Definition for a binary tree node. |
| 36 | + * function TreeNode(val) { |
| 37 | + * this.val = val; |
| 38 | + * this.left = this.right = null; |
| 39 | + * } |
| 40 | + */ |
| 41 | +/** |
| 42 | + * @param {TreeNode} root |
| 43 | + * @return {number[]} |
| 44 | + */ |
| 45 | +var preorderTraversal = function (root) { |
| 46 | + if (!root) return []; |
| 47 | + let res = []; |
| 48 | + let fun = (root) => { |
| 49 | + if (root) res.push(root.val); |
| 50 | + root.left && fun(root.left); |
| 51 | + root.right && fun(root.right); |
| 52 | + } |
| 53 | + fun(root); |
| 54 | + return res; |
| 55 | +}; |
| 56 | +``` |
| 57 | + |
| 58 | +**迭代做法** |
| 59 | + |
| 60 | +```javascript |
| 61 | +/** |
| 62 | + * Definition for a binary tree node. |
| 63 | + * function TreeNode(val) { |
| 64 | + * this.val = val; |
| 65 | + * this.left = this.right = null; |
| 66 | + * } |
| 67 | + */ |
| 68 | +/** |
| 69 | + * @param {TreeNode} root |
| 70 | + * @return {number[]} |
| 71 | + */ |
| 72 | +var preorderTraversal = function (root) { |
| 73 | + if (!root) return []; |
| 74 | + let res = []; |
| 75 | + let queue = [root]; |
| 76 | + while (queue.length) { |
| 77 | + let size = queue.length; |
| 78 | + while (size--) { |
| 79 | + // 取左孩子 |
| 80 | + let node = queue.pop(); |
| 81 | + res.push(node.val); |
| 82 | + // 优先放右孩子 |
| 83 | + node.right && queue.push(node.right); |
| 84 | + node.left && queue.push(node.left); |
| 85 | + } |
| 86 | + } |
| 87 | + return res; |
| 88 | +}; |
| 89 | +``` |
| 90 | + |
| 91 | +## 最后 |
| 92 | +文章产出不易,还望各位小伙伴们支持一波! |
| 93 | + |
| 94 | +往期精选: |
| 95 | + |
| 96 | +<a href="https://github.com/Chocolate1999/Front-end-learning-to-organize-notes">小狮子前端の笔记仓库</a> |
| 97 | + |
| 98 | +<a href="https://github.com/Chocolate1999/leetcode-javascript">leetcode-javascript:LeetCode 力扣的 JavaScript 解题仓库,前端刷题路线(思维导图)</a> |
| 99 | + |
| 100 | +小伙伴们可以在Issues中提交自己的解题代码,🤝 欢迎Contributing,可打卡刷题,Give a ⭐️ if this project helped you! |
| 101 | + |
| 102 | + |
| 103 | +<a href="https://yangchaoyi.vip/">访问超逸の博客</a>,方便小伙伴阅读玩耍~ |
| 104 | + |
| 105 | + |
| 106 | + |
| 107 | +```javascript |
| 108 | +学如逆水行舟,不进则退 |
| 109 | +``` |
| 110 | + |
| 111 | + |
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