94. Binary Tree Inorder Traversal

[Tcdian]

94. Binary Tree Inorder Traversal

给定一个二叉树，返回它的 中序 遍历。

Example

Input: [1,null,2,3]
   1
    \
     2
    /
   3

Output: [1,3,2]

Follow up

• 递归算法很简单，你可以通过迭代算法完成吗？

[Tcdian]

Solution 1 ( 递归 )

• JavaScript Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var inorderTraversal = function(root) {
    const result = [];
    inorder(root);
    return result;

    function inorder(root) {
        if (root === null) {
            return;
        }
        inorder(root.left);
        result.push(root.val);
        inorder(root.right);
    }
};

• TypeScript Solution

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function inorderTraversal(root: TreeNode | null): number[] {
    const result: number[] = [];
    inorder(root);
    return result;

    function inorder(root: TreeNode | null) {
        if (root === null) {
            return;
        }
        inorder(root.left);
        result.push(root.val);
        inorder(root.right);
    }
};

Solution 2 ( 迭代 )

• JavaScript Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var inorderTraversal = function(root) {
    if (root === null) {
        return [];
    }
    const result = [];
    const stack = [];
    let patrol = root;
    while (patrol !== null || stack.length !== 0) {
        while (patrol !== null) {
            stack.push(patrol);
            patrol = patrol.left;
        }
        patrol = stack.pop();
        result.push(patrol.val);
        patrol = patrol.right;
    }
    return result;
};

• TypeScript Solution

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function inorderTraversal(root: TreeNode | null): number[] {
    if (root === null) {
        return [];
    }
    const result: number[] = [];
    const stack: TreeNode[] = [];
    let patrol: TreeNode | null = root;
    while (patrol !== null || stack.length !== 0) {
        while (patrol !== null) {
            stack.push(patrol);
            patrol = patrol.left;
        }
        patrol = stack.pop()!;
        result.push(patrol.val);
        patrol = patrol.right;
    }
    return result;
};