Tag: java
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Find if a linked list is a palindrome or not
Problem: Given the head of a linked list , find if it is a palindrome or not. Find the solution in O(n) time and in place (O(1) space complexity) For example , the below linked list : 1 -> 2 -> 2 -> 1 is a palindrome The below is not: 1 -> 5 ->…
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Convert Excel Sheet Column Title to Number
Problem: Given an excel sheet column title , convert it to the column value. For example, Column value of sheet number ‘A’ is 1 ‘Z’ is 26 ‘AA’ is 27 ‘BA’ is 53 and so on. Constraints: Try out the solution here; https://leetcode.com/problems/excel-sheet-column-number/ Solution: If it is a single letter we can return the value…
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First Unique Character in a String
Given a string find the index of the first unique character (non repeating). For example, For the string “see” the output is 0 since the letter s is not repeated in the string For the string “bbaaddavt” the output is 7 because the letter v is not repeated and is present in index 7. Assumption:…
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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…
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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…
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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.…
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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…
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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…
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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…
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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…
