'I prefer to be true to myself, even at the hazard of incurring the ridicule of others, rather than to be false, and incur my own abhorrence.' -Frederick Douglass, Narrative of the Life of Frederick Douglass

Insertion Sort

by Ethan Glover, Sun, Oct 12, 2014 - (Edited) Sun, Oct 12, 2014

Tracing this program can be a little complex. But basically if a(i) is greater than the key, it copies a(i) to where the key is while saving the key in it's own variable. The program continues to do this backwards, shifting the array to the right as far as it needs. Once that is complete the key is inserted into the proper spot.

If we have the array [5, 2, 4, 6, 1, 3] a step by step tracing should reveal the following pattern.

First while loop:

[5, 5, 4, 6, 1, 3] (Notice how the key 2 is temporarily gone from the array.)
[2, 5, 4, 6, 1 , 3]

Second:

[2, 5, 5, 6, 1, 3]
[2, 4, 5, 6, 1, 3]
[2, 4, 5, 6, 1, 3]
[2, 4, 5, 6, 6, 3]
[2, 4, 4, 5, 6, 3]
[2, 2, 4, 5, 6, 3]
[1, 2, 4, 5, 6, 3]
[1, 2, 4, 5, 6, 6]
[1, 2, 4, 5, 5, 6]
[1, 2, 4, 4, 5, 6]
[1, 2, 3, 4, 5, 6]
[1, 2, 3, 4, 5, 6]

Note: To change the algorithm from increasing to decreasing order, all you have to change comparison operator on line 6 between a(i) and "key" to less than (<) from greater than (>).