# Sort algorithm--insert Sort

Source: Internet
Author: User

First, insert sort (insertion sort)

void  insertionsort (vector<int  > &a) { for  (int  i=1 ; i<a.size (); ++i) {int  tmp=a[i];        int   J;  for  (J=i;j>0  &&tmp< A[j-1 ];--j) {a[j]  =a[j-1  ];  //  insert tmp in the correct location  A[j]=TMP; }      }

Ideas:

each time a record to be sorted is inserted in its size into the previously ordered Subsequence (with the fact that the element on the known position 0 to position i-1 is already in an ordered state)

Process:

1) Initially, A[0] into an orderly area, a[1,...., N-1] is a disorderly area, so that I=1

2) Merge A[i] into the current ordered area a[0,..., I-1], forming a new ordered area a[0,...., i]

Select the first a[i of the unordered area] as TMP, compare with the ordered area, move all elements greater than TMP (before position I) to the right, stop when a[j]<tmp is found, insert tmp at A[J+1]

3) I plus 1, repeat 2), until finished a[n-1], sort complete

Complexity of Time:

1) within the cycle, the number of tests for each I value is i+1 times (when the input is reversed), the number of tests in the inner loop is (2+3+...+n) =θ (N2);

2) If the input is ordered (positive order), then the inner loop is not executed, the running time is O (N);

The average run time is O (N2).

Second, the shell sort

Sort algorithm--insert Sort

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