Basic Algorithms on Arrays

Learning ObjectivesArrays are useful for storing data in a linear

structureWe learn how to process data stored in an

arrayWe 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……

We recall an Array 10 20 60 30 67 90 76 65 87 07

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

Define and initialize an array10 20 60 30 67 90 76 65 87 07

int[ ] A = new int[10];A[0] = 10;A[1] = 20;

…..

Arrays are Static10

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Once defined

Size cannot be

changed

A.length = 20; /* illegal */

A

Why?Because a Static Memory Block is already

allocated and it cannot be changed.

So how do we change size?10

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double the size

int[ ] B = new int[2*A.length];for (int i=0; i<A.length; i++){ B[i] = A[i];}A = B;

Define a new array B of double the size

Iterate through the array A

Copy old elements of A to B

Discard old A and assign new B to A

Operations on Arrays

Iterate through all elements in the array

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for (int i =0; i < A.length; i = i + 1) { /* write your code here */ }

Iterate backwards10 20 60 30 67 90 76 65 87 07

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

Reverse the Array10 20 60 30 67 90 76 65 87 07

Think of an algorithm to do this

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Find the max/min in an Array10 20 60 30 67 90 76 65 87 07

for (int i = 0; i < A.length ; i = i + 1) {

}

Array of Stringsaaa ade 6as

dbb tr ori

ohelp

me yes no

for (int i = 0; i < A.length ; i = i + 1) {

}

Print allStrings starting

with prefix

Now to class work

NextLinear and Binary Search on Arrays