Difference between revisions of "W2202 Insertion Sort"
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Array: [33, 47, 62, 89, 95] | Swaps: 1 | Array: [33, 47, 62, 89, 95] | Swaps: 1 | ||
</pre> | </pre> | ||
== Quiz == | |||
<quiz shuffleanswers=true display=simple> | |||
{ | |||
Insertion Sort is an algorithm that selects the smallest element from an unsorted list in each iteration and places that element at the beginning of the unsorted list. | |||
|type="()"} | |||
- True | |||
+ False | |||
{ | |||
In which case would an insertion sort perform best? | |||
|type="()"} | |||
- These will all perform equally well | |||
- If the array was sorted in reverse order | |||
+ If the array was already sorted | |||
- If the array was in a random order | |||
{ | |||
One advantage of insertion sort is that it only requires one comparison. | |||
|type="()"} | |||
+ True | |||
- False | |||
{ | |||
Insertion sort is recommended for large arrays. | |||
|type="()"} | |||
- True | |||
+ False | |||
{ | |||
Insertion sort is useful when the array is close to being sorted. | |||
|type="()"} | |||
+ True | |||
- False | |||
{ | |||
Elements can move toward the beginning of the list very quickly. | |||
|type="()"} | |||
+ True | |||
- False | |||
{ | |||
Consider the list: 10, -59, 511, 831, -982<br/> | |||
After the '''first insertion''', the list will be: | |||
|type="()"} | |||
+ -59, 10, 511, 831, -982 | |||
- -982, 10, -59, 511, 831 | |||
- -59, 511, 10, 831, -932 | |||
- -982, -59, 10, 511, 831 | |||
{ | |||
Consider the list: 10, -59, 511, 831, -982<br/> | |||
After the '''second insertion''', the list will be: | |||
|type="()"} | |||
- -59, 10, 511, 831, -982 | |||
- -982, 10, -59, 511, 831 | |||
+ -59, 10, 511, 831, -932 | |||
- -982, -59, 10, 511, 831 | |||
{ | |||
Consider the list: 10, -59, 511, 831, -982<br/> | |||
After the '''third insertion''', the list will be: | |||
|type="()"} | |||
- -59, 10, 511, 831, -982 | |||
- -982, 10, -59, 511, 831 | |||
+ -59, 10, 511, 831, -932 | |||
- -982, -59, 10, 511, 831 | |||
{ | |||
Consider the list: 10, -59, 511, 831, -982<br/> | |||
After the '''first pass''', the list will be: | |||
|type="()"} | |||
+ -59, 10, 511, 831, -982 | |||
- -982, 10, -59, 511, 831 | |||
- -59, 511, 10, 831, -932 | |||
- -982, -59, 10, 511, 831 | |||
{ | |||
Consider the list: 10, -59, 511, 831, -982<br/> | |||
After the '''fourth pass''', the list will be: | |||
|type="()"} | |||
- -59, 10, 511, 831, -982 | |||
- -982, 10, -59, 511, 831 | |||
- -59, 10, 511, 831, -932 | |||
+ -982, -59, 10, 511, 831 | |||
{ | |||
Consider the list: -365, -894, 638, 678, -41<br/> | |||
How many passes are required before the algorithm terminates? | |||
|type="()"} | |||
- Two | |||
- Three | |||
+ Four | |||
- Five | |||
</quiz> | |||
== References == | == References == | ||
[https://en.wikipedia.org/wiki/Insertion_sort Insertion Sort] (Wikipedia) | [https://en.wikipedia.org/wiki/Insertion_sort Insertion Sort] (Wikipedia) |
Revision as of 18:13, 11 March 2021
Algorithm[edit]
Unlike Bubble Sort which only compares two elements at a time, insertion sort works by looking at each element and finding where it belongs in the sorted array. At its base, insertion sort is more complicated than bubble sort, but not by much:
- Iterate over the array
- For each element at index i, loop back through the array starting at i to 0
- Similar to bubble sort, if the element on the left is larger than the element on the right, swap them
- Because this starts by comparing i and i - 1, if the current element is not in place it will get swapped to i - 1. If it is still not in place in the next iteration, it will be swapped to i - 2, and so on until it is in the correct place
- Similar to bubble sort, if the element on the left is larger than the element on the right, swap them
- After each iteration, all of the elements up to i + 1 will be in the correct order although not necessarily sorted in the context of the full array
- Unlike bubble sort, you only need to iterate through the array once. Once you reach the end, the array is sorted
Swap[edit]
You can use the same swap function as in bubble sort because you only need to be able to swap two adjacent elements at a time.
Performance Considerations[edit]
Similar to bubble sort, if you use a swap function then consider passing the array by reference instead of by value to avoid copying the entire array for each swap.
Additionally, in insertion sort, you can stop/break the inner loop once you reach two sorted elements. In other words, you only need to swap until the element on the left is smaller than the element on the right, at which point you can exit the loop.
Example[edit]
Here is an example with an array of 5 elements:
Array: [95, 47, 62, 33, 89] | Initial * Elements at indexes 0 (95) and 1 (47) are not in order (95 > 47), swapping. Array: [47, 95, 62, 33, 89] | Swaps: 1 * Elements at indexes 1 (95) and 2 (62) are not in order (95 > 62), swapping. * Elements at indexes 0 (47) and 1 (62) are already in order (47 < 62), nothing to swap Array: [47, 62, 95, 33, 89] | Swaps: 1 * Elements at indexes 2 (95) and 3 (33) are not in order (95 > 33), swapping. * Elements at indexes 1 (62) and 2 (33) are not in order (62 > 33), swapping. * Elements at indexes 0 (47) and 1 (33) are not in order (47 > 33), swapping. Array: [33, 47, 62, 95, 89] | Swaps: 3 * Elements at indexes 3 (95) and 4 (89) are not in order (95 > 89), swapping. * Elements at indexes 2 (62) and 3 (89) are already in order (62 < 89), nothing to swap Array: [33, 47, 62, 89, 95] | Swaps: 1
Quiz[edit]
References[edit]
Insertion Sort (Wikipedia)