## Count number of ways to cover a distance

Title: Count number of ways to cover a distance Source: www.geeksforgeeks.org Given a distance ‘dist, count total number of ways to cover the distance with 1, 2 and 3 steps. Java solution Java /* http://www.geeksforgeeks.org/count-number-of-ways-to-cover-a-distance/ */ class CountWaysToCoverDistance { public int count(int dist) { if(dist==0) return 1; if(dist < 0) return 0; return count(dist-1) + ...

## Maximum Depth of Binary Tree

Title: Maximum Depth of Binary Tree Source: leetcode.com 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. Python solution Python ''' https://leetcode.com/problems/maximum-depth-of-binary-tree/ ''' # Definition for a binary tree node. # class TreeNode(object): # ...

## Detect Cycle in a Directed Graph1

Title: Detect Cycle in a Directed Graph Source: www.geeksforgeeks.org Given a directed graph, check whether the graph contains a cycle or not. Your function should return true if the given graph contains at least one cycle, else return false. For example, the following graph contains three cycles 0->2->0, 0->1->2->0 and 3->3, so your function must ...

## Fancy Numbers

Title: Check if a given number is Fancy Source: www.geeksforgeeks.org A fancy number is one which when rotated 180 degrees is the same. Given a number, find whether it is fancy or not. 180 degree rotations of 6, 9, 1, 0 and 8 are 9, 6, 1, 0 and 8 respectively Examples: Input: num = ...

## Design a tiny URL or URL shortener11

Title: How to design a tiny URL or URL shortener? Source: www.geeksforgeeks.org How to design a system that takes big URLs like “http://www.geeksforgeeks.org/count-sum-of-digits-in-numbers-from-1-to-n/” and converts them into a short 6 character URL. It is given that URLs are stored in database and every URL has an associated integer id. One important thing to note is, ...

## Determine if a binary tree is height-balanced

Title: How to determine if a binary tree is height-balanced? Source: www.geeksforgeeks.org A tree where no leaf is much farther away from the root than any other leaf. Different balancing schemes allow different definitions of “much farther” and different amounts of work to keep them balanced. Consider a height-balancing scheme where following conditions should be ...

## Rat in a Maze

Title: Rat in a Maze Source: www.geeksforgeeks.org Let us discuss Rat in a Maze as another example problem that can be solved using Backtracking. A Maze is given as N*N binary matrix of blocks where source block is the upper left most block i.e., maze[0][0] and destination block is lower rightmost block i.e., maze[N-1][N-1]. A ...

## Check if a binary tree is BST

Title: A program to check if a binary tree is BST or not Source: www.geeksforgeeks.org A binary search tree (BST) is a node based binary tree data structure which has the following properties. • The left subtree of a node contains only nodes with keys less than the node’s key. • The right subtree of ...

## Determine two trees are Same Tree

Title: Same Tree Source: leetcode.com Given two binary trees, write a function to check if they are equal or not. Two binary trees are considered equal if they are structurally identical and the nodes have the same value. Python solution Python ''' https://leetcode.com/problems/same-tree/ ''' # Definition for a binary tree node. # class TreeNode(object): # ...

## Sum Root to Leaf Numbers1

Title: Sum Root to Leaf Numbers Source: leetcode.com Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. An example is the root-to-leaf path 1->2->3 which represents the number 123. Find the total sum of all root-to-leaf numbers. For example, 1 / \ 2 3 123     1   / \  2   ...