Common sorting algorithms-fast sorting

Principles of fast sorting:

First, find a baseline value, which is equal to a certain element value. traverse the array and divide the array into two parts: smaller than the baseline value and greater than the baseline value. Then, sort the two parts quickly and recursively.

 

When the array is separated, a pointer is maintained pointing to the last element that has been found in a small part; a pointer is used for traversing.

 

Unstable sorting algorithm. When the array is ordered, the time complexity is the worst, Which is O (n2). The average and Optimal Values are O (N lgn ).

 

The Code is as follows:

1 # include <iostream> 2 using namespace STD; 3 4 template <typename T> 5 void quicksort (T num [], int first, int last) 6 {7 if (first> = last) 8 return; 9 10 t pviot = num [first]; 11 12 INT small = first; // pointer, point to the last value of a small part that has been processed 13 14 for (INT I = first + 1; I <= last; ++ I) 15 {16 if (Num [I] <= pviot) 17 {18 ++ small; // exchange the first value after a small part with the value smaller than the value found by the packettle 19 if (small <I) 20 {21 swap (Num [small], num [I]); 22} 23} 24} 25 26 swap (Num [first], num [small]); 27 28 quicksort (Num, first, small-1); 29 quicksort (Num, small + 1, last); 30} 31 32 int main () 33 {34 const int n = 5; 35 36 int Ia [N] = {1, 3, 6, 2, 4}; 37 double da [N] = {1.2, 3.4, 6.7, 2.3}; 38 39 quicksort (IA, 0, n-1 ); 40 quicksort (DA, 0, n-1); 41 42 for (INT I = 0; I <n; ++ I) 43 cout <Ia [I] <''; 44 cout <Endl; 45 46 for (INT I = 0; I <n; ++ I) 47 cout <da [I] <''; 48 cout <Endl; 49 50 return 0; 51}