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1305. 两棵二叉搜索树中的所有元素

题目描述

给你 root1 和 root2 这两棵二叉搜索树。请你返回一个列表，其中包含 两棵树 中的所有整数并按 升序 排序。.

 

示例 1：

输入：root1 = [2,1,4], root2 = [1,0,3]
输出：[0,1,1,2,3,4]

示例 2：

输入：root1 = [1,null,8], root2 = [8,1]
输出：[1,1,8,8]

 

提示：

  • 每棵树的节点数在 [0, 5000] 范围内
  • -105 <= Node.val <= 105

解法

方法一：DFS + 归并

由于两棵树都是二叉搜索树，所以我们可以通过中序遍历得到两棵树的节点值序列 $\textit{a}$ 和 $\textit{b}$，然后使用双指针归并两个有序数组，得到最终的答案。

时间复杂度 $O(n+m)$，空间复杂度 $O(n+m)$。其中 $n$ 和 $m$ 分别是两棵树的节点数。

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# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def getAllElements(
        self, root1: Optional[TreeNode], root2: Optional[TreeNode]
    ) -> List[int]:
        def dfs(root: Optional[TreeNode], nums: List[int]) -> int:
            if root is None:
                return
            dfs(root.left, nums)
            nums.append(root.val)
            dfs(root.right, nums)

        a, b = [], []
        dfs(root1, a)
        dfs(root2, b)
        m, n = len(a), len(b)
        i = j = 0
        ans = []
        while i < m and j < n:
            if a[i] <= b[j]:
                ans.append(a[i])
                i += 1
            else:
                ans.append(b[j])
                j += 1
        while i < m:
            ans.append(a[i])
            i += 1
        while j < n:
            ans.append(b[j])
            j += 1
        return ans

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Integer> getAllElements(TreeNode root1, TreeNode root2) {
        List<Integer> a = new ArrayList<>();
        List<Integer> b = new ArrayList<>();
        dfs(root1, a);
        dfs(root2, b);
        int m = a.size(), n = b.size();
        int i = 0, j = 0;
        List<Integer> ans = new ArrayList<>();
        while (i < m && j < n) {
            if (a.get(i) <= b.get(j)) {
                ans.add(a.get(i++));
            } else {
                ans.add(b.get(j++));
            }
        }
        while (i < m) {
            ans.add(a.get(i++));
        }
        while (j < n) {
            ans.add(b.get(j++));
        }
        return ans;
    }

    private void dfs(TreeNode root, List<Integer> nums) {
        if (root == null) {
            return;
        }
        dfs(root.left, nums);
        nums.add(root.val);
        dfs(root.right, nums);
    }
}

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> getAllElements(TreeNode* root1, TreeNode* root2) {
        vector<int> a, b, ans;
        dfs(root1, a);
        dfs(root2, b);

        int i = 0, j = 0;
        while (i < a.size() && j < b.size()) {
            if (a[i] <= b[j]) {
                ans.push_back(a[i++]);
            } else {
                ans.push_back(b[j++]);
            }
        }
        while (i < a.size()) {
            ans.push_back(a[i++]);
        }
        while (j < b.size()) {
            ans.push_back(b[j++]);
        }
        return ans;
    }

private:
    void dfs(TreeNode* root, vector<int>& nums) {
        if (root == nullptr) {
            return;
        }
        dfs(root->left, nums);
        nums.push_back(root->val);
        dfs(root->right, nums);
    }
};

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/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func getAllElements(root1 *TreeNode, root2 *TreeNode) (ans []int) {
    var dfs func(*TreeNode, *[]int)
    dfs = func(root *TreeNode, nums *[]int) {
        if root == nil {
            return
        }
        dfs(root.Left, nums)
        *nums = append(*nums, root.Val)
        dfs(root.Right, nums)
    }
    a, b := []int{}, []int{}
    dfs(root1, &a)
    dfs(root2, &b)
    i, j := 0, 0
    m, n := len(a), len(b)
    for i < m && j < n {
        if a[i] < b[j] {
            ans = append(ans, a[i])
            i++
        } else {
            ans = append(ans, b[j])
            j++
        }
    }
    for ; i < m; i++ {
        ans = append(ans, a[i])
    }
    for ; j < n; j++ {
        ans = append(ans, b[j])
    }
    return
}

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/**
 * 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 getAllElements(root1: TreeNode | null, root2: TreeNode | null): number[] {
    const dfs = (root: TreeNode | null, nums: number[]) => {
        if (!root) {
            return;
        }
        dfs(root.left, nums);
        nums.push(root.val);
        dfs(root.right, nums);
    };
    const a: number[] = [];
    const b: number[] = [];
    dfs(root1, a);
    dfs(root2, b);
    const [m, n] = [a.length, b.length];
    const ans: number[] = [];
    let [i, j] = [0, 0];
    while (i < m && j < n) {
        if (a[i] < b[j]) {
            ans.push(a[i++]);
        } else {
            ans.push(b[j++]);
        }
    }
    while (i < m) {
        ans.push(a[i++]);
    }
    while (j < n) {
        ans.push(b[j++]);
    }
    return ans;
}

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// Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
//
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }
use std::cell::RefCell;
use std::rc::Rc;
impl Solution {
    pub fn get_all_elements(
        root1: Option<Rc<RefCell<TreeNode>>>,
        root2: Option<Rc<RefCell<TreeNode>>>,
    ) -> Vec<i32> {
        let mut a = Vec::new();
        let mut b = Vec::new();

        Solution::dfs(&root1, &mut a);
        Solution::dfs(&root2, &mut b);

        let mut ans = Vec::new();
        let (mut i, mut j) = (0, 0);

        while i < a.len() && j < b.len() {
            if a[i] <= b[j] {
                ans.push(a[i]);
                i += 1;
            } else {
                ans.push(b[j]);
                j += 1;
            }
        }

        while i < a.len() {
            ans.push(a[i]);
            i += 1;
        }

        while j < b.len() {
            ans.push(b[j]);
            j += 1;
        }

        ans
    }

    fn dfs(root: &Option<Rc<RefCell<TreeNode>>>, nums: &mut Vec<i32>) {
        if let Some(node) = root {
            let node = node.borrow();
            Solution::dfs(&node.left, nums);
            nums.push(node.val);
            Solution::dfs(&node.right, nums);
        }
    }
}

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