ZQYnn's blog

101. Symmetric TreeGiven a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).For example, this binary tree [1,2,2,3,4,4,3] is symmetric: 1 / \ 2 2 /...

The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.Given an integer n, return all distinct solutions to the n-queens puzzle.Each s...

Reverse StringWrite a function that reverses a string. The input string is given as an array of characters char[].Do not allocate extra space for another array, you must do this by modifying the inp...

Kth Smallest Element in a BSTGiven a binary search tree, write a function kthSmallest to find the kth smallest element in it.Note:You may assume k is always valid, 1 ≤ k ≤ BST’s total elements.Ex...

Validate Binary Search TreeGiven a binary tree, determine if it is a valid binary search tree (BST).Assume a BST is defined as follows:The left subtree of a node contains only nodes with keys l...

Maximum Depth of Binary TreeGiven 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 ...

Binary Tree Inorder TraversalGiven a binary tree, return the inorder traversal of its nodes’ values.Example:Input: [1,null,2,3] 1 \ 2 / 3Output: [1,3,2]Follow up: Recursive...

Balanced Binary TreeGiven a binary tree, determine if it is height-balanced.For this problem, a height-balanced binary tree is defined as:a binary tree in which the depth of the two subtrees of...

Binary Tree PathsGiven a binary tree, return all root-to-leaf paths.Note: A leaf is a node with no children.Example:Input: 1 / \2 3 \ 5Output: ["1->2->5", "1->3"]Expl...

Same TreeGiven two binary trees, write a function to check if they are the same or not.Two binary trees are considered the same if they are structurally identical and the nodes have the same value....

Minimum Depth of Binary TreeGiven 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 ...

Find Largest Value in Each Tree RowExample:Input: 1 / \ 3 2 / \ \ 5 3 9 Output: [1, 3, 9]You need to find the largest value in each row of a b...

Find Bottom Left Tree ValueGiven a binary tree, find the leftmost value in the last row of the tree.Example 1:Input: 2 / \ 1 3Output:1Example 2:Input: 1 / \ ...

Binary Tree Right Side ViewGiven a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.Example:Input: [1,2,3,nul...

Number of IslandsGiven a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertic...

Path SumGiven a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.Note: A leaf is a node with no children....

Binary Tree Level Order TraversalGiven a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).For example:Given binary tree [3,9,20,null,nul...

Write a program to solve a Sudoku puzzle by filling the empty cells.A sudoku solution must satisfy all of the following rules:Each of the digits 1-9 must occur exactly once in each row.Each of the...