CS157

CS157: Intro to C, Part II

Spring 2018

Sorting

See this page as a slide show

Searching and Sorting arrays

CS157 Sorting

Searching & Sorting methodologies

Linear Search

The easiest algorithm is a Linear Search:

Linear Search

#define SIZE 7
int arr[SIZE] = {1, 99, 25, 68, 92, 38, 74};
int key = 68;       // searching for this
int where = -1;     // Where we found it
for (int i=0; i<SIZE; i++) {
    if (arr[i] == key) {
        where = i;
        break;
    }
}
if (where == -1)
    printf("Sorry, %d not found in list\n", key);
else
   printf("%d found at position %d\n", key, where);
68 found at position 3

Binary Search

Binary search, on the other hand, is smarter. It takes advantage of the fact that the data that you’re searching is sorted already.

Binary Search

#define SIZE 7
int arr[SIZE] = {1, 25, 38, 68, 74, 92, 99};
int key = 68;       // searching for this
int low=0, mid, high=SIZE-1;
while (low <= high) {
    mid = (low+high) / 2;
    if (arr[mid] == key)
        break;
    else if (arr[mid] > key)
        high = mid-1;
    else
        low = mid+1;
}
if (low <= high)
   printf("%d found at position %d\n", key, mid);
else
    printf("Sorry, %d not found in list\n", key);
68 found at position 3

Sorting

Selection Sort

Selection Sort

Original: 3  9  6  1  2 
Smallest unsorted is 1; swap with first unsorted, 3: 1  9  6  3  2 
Smallest unsorted is 2; swap with first unsorted, 9: 1  2  6  3  9 
Smallest unsorted is 3; swap with first unsorted, 6: 1  2  3  6  9 
Smallest unsorted is 6; swap with first unsorted, 6: 1  2  3  6  9 

Swapping

temp = first;
first = second;
second = temp;

Insertion Sort

Insertion Sort

Original:  3    9    6    1    2  
After inserting 9:  3    9    6    1    2  
After inserting 6:  3    6    9    1    2  
After inserting 1:  1    3    6    9    2  
After inserting 2:  1    2    3    6    9  

Comparing Sorts

Bubble Sort

Bubble Sort

Bubbling largest element to the end of the list:

Original:  3    9    6    1    2  
After pass 1:  3    6    1    2    9  
After pass 2:  3    1    2    6    9  
After pass 3:  1    2    3    6    9  
After pass 4:  1    2    3    6    9  

Bubble Sort

Bubbling smallest element to the front of the list:

Original:  3    9    6    1    2  
After pass 1:  1    3    9    6    2  
After pass 2:  1    2    3    9    6  
After pass 3:  1    2    3    6    9  
After pass 4:  1    2    3    6    9  

Bubble Sort

#define SIZE 7
int arr[SIZE] = {1, 99, 25, 68, 92, 38, 74};

for (int i=1; i<SIZE; i++)
    for (int j=0; j<SIZE-i; j++)
        if (arr[j] > arr[j+1])
            swap(arr, j, j+1);
for (int i=0; i<SIZE; i++)
    printf("%d\n", arr[i]);

Modified: 2016-11-18T12:49

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