# Three implementations of two direct insertion sequences for vernacular classical algorithm series

Source: Internet
Author: User

The basic idea of a direct insert sort (insertion sort) is to insert a record to be sorted each time, by its keyword size, into the appropriate position in the previously ordered subsequence until all the records have been inserted.

Set the array to a[0...n-1].

1. Initially, a[0] self into 1 ordered areas, unordered area is a[1..n-1]. Make I=1

2. Merge A[i] into an ordered interval of A[0...I] formed in the current ordered region A[0...i-1].

3. i++ and repeat the second step until the i==n-1. Sorting is complete.

The following code is written in strict accordance with the definition (from small to large sort):

`void Insertsort1 (int a[], int n) {int I, J, k;for (i = 1; i < n; i++) {//= A[i] Find an appropriate position for (j = a[0...i-1) in the ordered interval of the preceding i-1] J >= 0;  j--) if (A[j] < a[i]) break;//If a suitable position is found if (j! = i-1) {//will be greater than a[i] data is moved backwards int temp = a[i];for (k = i-1; k > J; k--) a[k + 1] = a[k];//put a[i] in the correct position a[k + 1] = temp;}}}`

This code is too long, not clear enough. Now make a rewrite, merging the two steps of search and data back. That is, each a[i] first and previous data a[i-1], assuming a[i] > a[i-1] Description a[0...i] is also ordered, without adjustment. otherwise j=i-1,temp=a[i]. Then move the data a[j] backward and forward, and when there is data a[j]<a[i] stop and drop the temp at A[j + 1].

`void Insertsort2 (int a[], int n) {int I, j;for (i = 1; i < n; i++) if (A[i] < a[i-1]) {int temp = a[i];for (j = i-1 ; J >= 0 && a[j] > temp; j--) A[j + 1] = a[j];a[j + 1] = temp;}}`

Then rewrite the method used to insert a[j] into the ordered interval of the previous a[0...j-1] and replace the data with data exchange. Suppose A[j] [previous data a[j-1] > A[j], swap a[j] and a[j-1], then j--until A[j-1] <= a[j]. This also enables the new data to be incorporated into an orderly interval.

`void Insertsort3 (int a[], int n) {int I, j;for (i = 1; i < n; i++) for (j = i-1; J >= 0 && A[j] > a[j + 1 ]; j--) Swap (A[j], a[j + 1]);}`

Three implementations of two direct insertion sequences for vernacular classical algorithm series

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