Author: Vijay SRJ
-
Find Peak element in an array
Problem: Given an integer array return the index of any peak element in it. Find a solution in O(logn) time. A peak element is an element which is greater than its neighbors. Its neighbors are the immediate elements to its left and right. you can return any peak element. So for example , if the…
-
Find first missing positive integer in an array.
Problem: Given an array of integers find the first missing positive integer . The first positive integer is 1. So if 1 is itself missing you need to return 1 else whatever number after 1 is missing that should be returned. For example, Given the array: [1,2,4,5] The output is 3 Given the array: [3,4,-1,1,5]…
-
Kth largest element in an array
Given an array of integers, find the kth largest element in the array. For example, Given the input [3,2,1,5,6,4] and k = 2 The output is 5 Try out the solution here: https://leetcode.com/problems/kth-largest-element-in-an-array/ Solution: We can solve this problem in multiple ways. Let’s look at three approaches. Approach 1 – Sort the array In this…
-
Sort three colors in an array
Given an array containing three different colors red ,white and blue denoted by numbers 0,1 and 2 sort the array such that red comes first followed by white followed by blue. Constraints: For example, Given the input: [2,0,1,0,2,1] The output is [0,0,1,1,2,2] Try out the solution here: https://leetcode.com/problems/sort-colors/ Solution: Approach 1 – Count the number…
-
Find the element which appears more than half the array size
Given an array, find the majority element which appears more than half the size of the array. Constraints: For example, in the below array: [7,6,8,7,7,7] The output is 7 since it appears 4 times which is more than half the size of the array (3) Solution: Finding a solution with O(n) extra space is easier.…
-
Single non duplicate number in an array
Given an array with all elements repeated twice except one element find out that element. Constraints: The time complexity should be O(n) Space complexity should be O(1) For example: Given the array : [1,3,4,3,4] the output is 1 since it occurs only once. Try out the solution here: https://leetcode.com/problems/single-number Solution: If we can use extra…
-
Is a Tree Symmetric?
Given a binary tree find out if it is symmetric or not. A tree is symmetric if it is left sub tree is a reflection of its right sub tree. Note that symmetry doesn’t mean left sub tree is equal to right sub tree. The following tree is a symmetric tree: As you see the…
-
Valid Sudoku
Given a board of size 9 * 9 representing a sudoku game , find out if it is valid. It is valid if : For example, The below sudoku: represented by the array: Input: board = [[“5″,”3″,”.”,”.”,”7″,”.”,”.”,”.”,”.”] ,[“6″,”.”,”.”,”1″,”9″,”5″,”.”,”.”,”.”] ,[“.”,”9″,”8″,”.”,”.”,”.”,”.”,”6″,”.”] ,[“8″,”.”,”.”,”.”,”6″,”.”,”.”,”.”,”3″] ,[“4″,”.”,”.”,”8″,”.”,”3″,”.”,”.”,”1″] ,[“7″,”.”,”.”,”.”,”2″,”.”,”.”,”.”,”6″] ,[“.”,”6″,”.”,”.”,”.”,”.”,”2″,”8″,”.”] ,[“.”,”.”,”.”,”4″,”1″,”9″,”.”,”.”,”5″] ,[“.”,”.”,”.”,”.”,”8″,”.”,”.”,”7″,”9″]] is valid since it obeys all the three conditions. Try…
-
Merge Sorted Array
Given two sorted arrays and their sizes , merge the two into the first sorted array. Extra space equal to the size of the second array is provided at the end of the first array. For example, Given the arrays: num1 = [1,2,3,0,0,0] , size = 3 ( remaining space for the second array to…
-
Inorder traversal of a Tree
Given the root node of a Tree , return the node values in a list in inorder. For example, For the below tree: The inorder traversal is [ 0,2,3,4,5,6,7,8,9] Try out the solution here: https://leetcode.com/problems/binary-tree-inorder-traversal Solution: There are three ways to do inorder traversal: Let’s look into each of them. Approach 1 – Recursion: In…
