Sorting

Leena A

PGT Comp SC

KV No:2 Jalahalli

Introduction

• Common problem: sort a list of values, starting from lowest to highest. – List of exam scores

– Words of dictionary in alphabetical order

– Students names listed alphabetically

– Student records sorted by ID#

Quadratic Sorting Algorithms

• We are given n records to sort.

Three Sorting techniques are used normally

– Selection sort– Insertion sort– Bubble sort

Sorting an Array of IntegersSorting an Array of Integers

• Example: we are given an array of six integers that we want to sort from smallest to largest

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• Start by finding the smallest entry.

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• Swap the smallest entry with the first entry.

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• Swap the smallest entry with the first entry.

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• Part of the array is now sorted.

Sorted side Unsorted side

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• Find the smallest element in the unsorted side.

Sorted side Unsorted side

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• Swap with the front of the unsorted side.

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• We have increased the size of the sorted side by one element.

Sorted side Unsorted side

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• The process continues...

Sorted side Unsorted side

Smallestfrom

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Smallestfrom

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• The process continues...

Sorted side Unsorted side

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Swap

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front

Swap

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• The process continues...

Sorted side Unsorted sideSorted side

is bigger

Sorted sideis bigger

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• The process keeps adding one more number to the sorted side.

• The sorted side has the smallest numbers, arranged from small to large.

Sorted side Unsorted side

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The Selection Sort AlgorithmThe Selection Sort Algorithm

• We can stop when the unsorted side has just one number, since that number must be the largest number.

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Sorted side Unsorted side

The Selection Sort AlgorithmThe Selection Sort Algorithm

• The array is now sorted.

• We repeatedly selected the smallest element, and moved this element to the front of the unsorted side. [0] [1] [2] [3] [4] [5]

void selectionsort(int a[], int size){int small,pos,t;for(int i=0;i<size;i++){small=a[i];for(int j= i+1;j<size;j++){

if(a[j]<small){small=a[j];pos=j;}

}t=a[i];a[i]=a[pos];a[pos]=t;}}

1. Write a function to sort the student records based on their marks in ascending order.

The records are implemented as followsstruct student

{int rno;char name[20];float marks;

};

Review Questions

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