Basic Algorithms on Arrays

1. Basic Algorithms on Arrays

2. Learning Objectives • Arrays are useful for storing data in a linear structure • We learn how to process data stored in an array • We learn how to • Read a file and store a set of Strings in an array • We learn how to find a specific String in an array • We learn how to find ALL Strings that starts with a prefix String • And more……

3. We recall an Array Characteristics - A contiguous block of memory spaces - Each one is referred to by an index - indices start from 0 and go to n-1 - Array is “homogeneous” , that is, it can only keep one type of data

4. Define and initialize an array int[ ] A = new int[10]; A[0] = 10; A[1] = 20; …..

5. Arrays are Static Once defined Size cannot be changed A A.length = 20; /* illegal */ Why? Because a Static Memory Block is already allocated and it cannot be changed.

6. So how do we change size? double the size Define a new array B of double the size int[ ] B = new int[2*A.length];for (inti=0; i<A.length; i++){ B[i] = A[i]; } A = B; Iterate through the array A Copy old elements of A to B Discard old A and assign new B to A

7. Operations on Arrays

8. Iterate through all elements in the array for (inti =0; i < A.length; i = i + 1) { /* write your code here */ }

9. Iterate backwards for (inti = A.length-1; i >= 0; i = i - 1) { /* write your code here */ }

10. Reverse the Array Think of an algorithm to do this

11. Find the max/min in an Array for (inti = 0; i < A.length ; i = i + 1) { }

12. Array of Strings for (inti = 0; i < A.length ; i = i + 1) { } Print all Strings starting with prefix

13. Now to class work

14. Next • Linear and Binary Search on Arrays