花花酱 LeetCode 958. Check Completeness of a Binary Tree

By zxi on December 18, 2018

Given a binary tree, determine if it is a complete binary tree.

Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2^h nodes inclusive at the last level h.

Example 1:

Input: [1,2,3,4,5,6]
Output: true
Explanation: Every level before the last is full (ie. levels with node-values {1} and {2, 3}), and all nodes in the last level ({4, 5, 6}) are as far left as possible.

Example 2:

Input: [1,2,3,4,5,null,7]
Output: false
Explanation: The node with value 7 isn't as far left as possible.

Note:

The tree will have between 1 and 100 nodes.

Solution:

Level order traversal, if any nodes appears after a missing node then the tree is not a perfect binary tree.

Time complexity: O(n)

Space complexity: O(n)

C++

class Solution {

public:

bool isCompleteTree(TreeNode* root) {

if (!root) return true;

queue<TreeNode> q;

q.push(root);

bool missing = false;

while (!q.empty()) {

auto size = q.size();

while (size--) {

auto node = q.front(); q.pop();

if (node) {

if (missing) return false;

q.push(node->left);

q.push(node->right);

} else {

missing = true;

}

return true;

}

};

Python3

class Solution:

def isCompleteTree(self, root):

if not root: return True

q = collections.deque([root])

missing = False

while q:

size = len(q)

while size > 0:

size -= 1

node = q.popleft()

if node:

if missing: return False

q.append(node.left)

q.append(node.right)

else:

missing = True

return True

花花酱 LeetCode Binary Trees 二叉树 SP12

By zxi on December 16, 2018

Binary tree is one of the most frequently asked question type during interview.

二叉树是面试中经常会问到的问题。

The candidate needs to understand the recursively defined TreeNode and solve the problem through recursion.

面试者需要理解递归定义的TreeNode数据类型，并且通过使用递归的方式来解决问题。

花花酱 LeetCode 111. Minimum Depth of Binary Tree

By zxi on December 15, 2018

Problem

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

return its minimum depth = 2.

Solution: Recursion

Time complexity: O(n)

Space complexity: O(n)

C++

// Author: Huahua, 4 ms

class Solution {

public:

int minDepth(TreeNode* root) {

if (!root) return 0;

if (!root->left && !root->right) return 1;

int l = root->left ? minDepth(root->left) : INT_MAX;

int r = root->right ? minDepth(root->right) : INT_MAX;

return min(l, r) + 1;

}

};

Python3

class Solution:

def minDepth(self, root):

if not root: return 0

if not root.left and not root.right: return 1

l = self.minDepth(root.left)

r = self.minDepth(root.right)

if not root.left: return 1 + r

if not root.right: return 1 + l

return 1 + min(l, r)

Problem

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

return its depth = 3.

Solution: Recursion

maxDepth(root) = max(maxDepth(root.left), maxDepth(root.right)) + 1

Time complexity: O(n)

Space complexity: O(n)

C++

// Author: Huahua, 4 ms

class Solution {

public:

int maxDepth(TreeNode* root) {

if (!root) return 0;

int l = maxDepth(root->left);

int r = maxDepth(root->right);

return max(l, r) + 1;

}

};

Python3

# Author: Huahua, 80 ms

class Solution:

def maxDepth(self, root):

if not root: return 0

l = self.maxDepth(root.left)

r = self.maxDepth(root.right)

return max(l, r) + 1

花花酱 LeetCode 919. Complete Binary Tree Inserter

By zxi on October 6, 2018

Problem

A complete binary tree is a binary tree in which every level, except possibly the last, is completely filled, and all nodes are as far left as possible.

Write a data structure CBTInserter that is initialized with a complete binary tree and supports the following operations:

CBTInserter(TreeNode root) initializes the data structure on a given tree with head node root;
CBTInserter.insert(int v) will insert a TreeNode into the tree with value node.val = v so that the tree remains complete, and returns the value of the parent of the inserted TreeNode;
CBTInserter.get_root() will return the head node of the tree.

Example 1:

Input: inputs = ["CBTInserter","insert","get_root"], inputs = [[[1]],[2],[]]
Output: [null,1,[1,2]]

Example 2:

Input: inputs = ["CBTInserter","insert","insert","get_root"], inputs = [[[1,2,3,4,5,6]],[7],[8],[]]
Output: [null,3,4,[1,2,3,4,5,6,7,8]]

Note:

The initial given tree is complete and contains between 1 and 1000 nodes.
CBTInserter.insert is called at most 10000 times per test case.
Every value of a given or inserted node is between 0 and 5000.

Solution 2: Deque

Using a deck to keep track of insertable nodes (potential parents) in order.

Time complexity: O(1) / O(n) first call

Space complexity: O(n)

C++

// Author: Huahua

class CBTInserter {

public:

CBTInserter(TreeNode* root): root_(root), d_({root}) {}

int insert(int v) {

while (!d_.empty()) {

TreeNode* r = d_.front();

if (r->left && r->right) {

d_.push_back(r->left);

d_.push_back(r->right);

d_.pop_front();

} else if (r->left) {

r->right = new TreeNode(v);

return r->val;

} else {

r->left = new TreeNode(v);

return r->val;

}

TreeNode* get_root() { return root_; }

private:

std::deque<TreeNode*> d_;

TreeNode* root_;

};

Posts tagged as “tree”

花花酱 LeetCode 958. Check Completeness of a Binary Tree

Solution:

C++

Python3

花花酱 LeetCode Binary Trees 二叉树 SP12

花花酱 LeetCode 111. Minimum Depth of Binary Tree

Problem

Solution: Recursion

C++

Python3

Related Problem

花花酱 LeetCode 104. Maximum Depth of Binary Tree

Problem

Solution: Recursion

C++

Python3

花花酱 LeetCode 919. Complete Binary Tree Inserter

Problem

Solution 2: Deque

C++