Category Archives: Data

PostgreSQL; Neo4j, Big Data

Maps in Java

Concrete maps in Java JDK 1.8 Below is the summary of differences between HashMap, LinkedHashMap, TreeMap, and Hashtable in Java: (Source: If we need to get the key back in insertion order, then use LinkedHashMap. If we need to get the key back in their true/natural order, then use TreeMap. Otherwise, HashMap is best because it… Read More »

Binary search algorithm

1. Getting. In binary search algorithm, we find an element x in a sorted array by using the principle of divide and conquer. First, we compare x to the middle point of the array. If x is less than the middle point, then we search the left of array. Otherwise, we look for the right… Read More »

Calculating Pi by Leibniz formular

Problem This is to calculate an approximation to the constant Pi (π). Solution 1.1. Computation  fomular will take O(m) steps –linear algorithm or time complexity is O(m) . The Leibniz series converges very slowly if m approaches infinity.  To calculate pi to one million decimal places would require 106 terms. 1.2 Calculate the nth digit of… Read More »

Heap’s algorithm for Permutations

Problem: Find the biggest number from the array [3, 1, 2] (n = 3). For example: 321 is largest number in comparison with all possible numbers from the array. Solving: We need to resolve 2 things. Final all possible Permutations from the array. So possible permutation is n! = 3! = 6 cases. Find a maximum number from… Read More »

Quick Sort Algorithm

Quick sort discovered by C.A.R Hoare in 1962. It is a fast algorithm for internal or in-memory sorting except for sorting data in disk files. Figure 1: Time and Space complexity of quick sort. There are three basic steps: Partition the array or sub-array into left (smaller keys) and right (larger keys) groups. Call ourselves to sort… Read More »