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Posts published in “Tree”

花花酱 LeetCode 1325. Delete Leaves With a Given Value

Given a binary tree root and an integer target, delete all the leaf nodes with value target.

Note that once you delete a leaf node with value targetif it’s parent node becomes a leaf node and has the value target, it should also be deleted (you need to continue doing that until you can’t).

Example 1:

Input: root = [1,2,3,2,null,2,4], target = 2
Output: [1,null,3,null,4]
Explanation: Leaf nodes in green with value (target = 2) are removed (Picture in left). 
After removing, new nodes become leaf nodes with value (target = 2) (Picture in center).

Example 2:

Input: root = [1,3,3,3,2], target = 3
Output: [1,3,null,null,2]

Example 3:

Input: root = [1,2,null,2,null,2], target = 2
Output: [1]
Explanation: Leaf nodes in green with value (target = 2) are removed at each step.

Example 4:

Input: root = [1,1,1], target = 1
Output: []

Example 5:

Input: root = [1,2,3], target = 1
Output: [1,2,3]

Constraints:

  • 1 <= target <= 1000
  • Each tree has at most 3000 nodes.
  • Each node’s value is between [1, 1000].

Solution: Recursion

Post-order traversal

Time complexity: O(n)
Space complexity: O(n)

C++

花花酱 LeetCode 1315. Sum of Nodes with Even-Valued Grandparent

Given a binary tree, return the sum of values of nodes with even-valued grandparent.  (A grandparent of a node is the parent of its parent, if it exists.)

If there are no nodes with an even-valued grandparent, return 0.

Example 1:

Input: root = [6,7,8,2,7,1,3,9,null,1,4,null,null,null,5]
Output: 18
Explanation: The red nodes are the nodes with even-value grandparent while the blue nodes are the even-value grandparents.

Constraints:

  • The number of nodes in the tree is between 1 and 10^4.
  • The value of nodes is between 1 and 100.

Solution: Recursion

Time complexity: O(n)
Space complexity: O(n)

C++

花花酱 LeetCode 1305. All Elements in Two Binary Search Trees

Given two binary search trees root1 and root2.

Return a list containing all the integers from both trees sorted in ascending order.

Example 1:

Input: root1 = [2,1,4], root2 = [1,0,3]
Output: [0,1,1,2,3,4]

Example 2:

Input: root1 = [0,-10,10], root2 = [5,1,7,0,2]
Output: [-10,0,0,1,2,5,7,10]

Example 3:

Input: root1 = [], root2 = [5,1,7,0,2]
Output: [0,1,2,5,7]

Example 4:

Input: root1 = [0,-10,10], root2 = []
Output: [-10,0,10]

Example 5:

Input: root1 = [1,null,8], root2 = [8,1]
Output: [1,1,8,8]

Constraints:

  • Each tree has at most 5000 nodes.
  • Each node’s value is between [-10^5, 10^5].

Solution: Inorder traversal + Merge Sort

Time complexity: O(t1 + t2)
Space complexity: O(t1 + t2)

C++

C++/STL

花花酱 LeetCode 1273. Delete Tree Nodes

A tree rooted at node 0 is given as follows:

  • The number of nodes is nodes;
  • The value of the i-th node is value[i];
  • The parent of the i-th node is parent[i].

Remove every subtree whose sum of values of nodes is zero.

After doing so, return the number of nodes remaining in the tree.

Example 1:

Input: nodes = 7, parent = [-1,0,0,1,2,2,2], value = [1,-2,4,0,-2,-1,-1]
Output: 2

Constraints:

  • 1 <= nodes <= 10^4
  • -10^5 <= value[i] <= 10^5
  • parent.length == nodes
  • parent[0] == -1 which indicates that 0 is the root.

Solution: Inorder Traversal

For each node, return the sum of all its subtrees and number of nodes including itself after removal.

Time complexity: O(n)
Space complexity: O(n)

C++

花花酱 LeetCode 1261. Find Elements in a Contaminated Binary Tree

Given a binary tree with the following rules:

  1. root.val == 0
  2. If treeNode.val == x and treeNode.left != null, then treeNode.left.val == 2 * x + 1
  3. If treeNode.val == x and treeNode.right != null, then treeNode.right.val == 2 * x + 2

Now the binary tree is contaminated, which means all treeNode.val have been changed to -1.

You need to first recover the binary tree and then implement the FindElements class:

  • FindElements(TreeNode* root) Initializes the object with a contamined binary tree, you need to recover it first.
  • bool find(int target) Return if the target value exists in the recovered binary tree.

Example 1:

Input
["FindElements","find","find"]
[[[-1,null,-1]],[1],[2]]
Output

[null,false,true]

Explanation FindElements findElements = new FindElements([-1,null,-1]); findElements.find(1); // return False findElements.find(2); // return True

Example 2:

Input
["FindElements","find","find","find"]
[[[-1,-1,-1,-1,-1]],[1],[3],[5]]
Output

[null,true,true,false]

Explanation FindElements findElements = new FindElements([-1,-1,-1,-1,-1]); findElements.find(1); // return True findElements.find(3); // return True findElements.find(5); // return False

Example 3:

Input
["FindElements","find","find","find","find"]
[[[-1,null,-1,-1,null,-1]],[2],[3],[4],[5]]
Output

[null,true,false,false,true]

Explanation FindElements findElements = new FindElements([-1,null,-1,-1,null,-1]); findElements.find(2); // return True findElements.find(3); // return False findElements.find(4); // return False findElements.find(5); // return True

Constraints:

  • TreeNode.val == -1
  • The height of the binary tree is less than or equal to 20
  • The total number of nodes is between [1, 10^4]
  • Total calls of find() is between [1, 10^4]
  • 0 <= target <= 10^6

Solutoin 1: Recursion and HashSet

Time complexity: Recover O(n), find O(1)
Space complexity: O(n)

C++

Solution 2: Recursion and Binary format

The binary format of t = (target + 1) (from high bit to low bit, e.g. in reverse order) decides where to go at each node.
t % 2 == 1, go right, otherwise go left
t = t / 2 or t >>= 1

Time complexity: Recover O(n), find O(log|target|)
Space complexity: O(1)

C++