Quick sorting)

AlgorithmReview.

Time Complexity:

Average O (N * log2n)

Worst case O (n2)

Preferably O (N * log2n)

Ideas:

Set the array to be sorted as A, with the length of N, starting with I = 0, j = n-1. For each round of fast sorting:

1. from the right to the left (j -- direction), find a value smaller than the key (generally set to a [0, then exchange a [I] with a [J.

2. Search for a value greater than the key from the left to the right (I ++ direction) and exchange a [I] with a [J.

3. Perform steps 1 and 2 until I> J. At this time, the left side of the key is a smaller value than the key, and the right side of the key is a greater value than the key. Then, the left half edge array and Right Half Edge array are recursion respectively. Stop recursion until the recursion termination condition (I> = J) is met.

Code:

# Include <iostream> Using   Namespace  STD;  /*  Output array elements in the specified range */  Void Showarray ( Int Arr [], Int Start, Int  End ){  For ( Int I = start; I <= end; I ++ ) {Cout <Arr [I] < "   "  ;} Cout < Endl ;}  /* Swap the values of elements in the array at the specified position  */  Void Swap ( Int Arr [], Int A, Int  B ){  Int Temp = 0  ; Temp = Arr [a]; arr [A] = Arr [B]; arr [B] = Temp ;}  /* Quick Sort Function  */  Void Sortunit ( Int Arr [], Int I, Int  J ){  If (I> = J ){  Return  ;}  Int Key = Arr [I];  Int Start = I; Int End = J;  Int Temp = 0  ;  While (I < J ){  While (ARR [J]> = Key & J> I) {J -- ;}  If (ARR [J] < Key) {swap (ARR, I, j );}  While (ARR [I] <= Key & I < J) {I ++ ;}  If (ARR [I]> Key) {swap (ARR, I, j );}}  Int Center = (I + J )/ 2  ;  /*  Auxiliary Function, check whether the output data is correct  */  Showarray (ARR, start, end); cout < "  Center Index = " <Center < "  , Center value =  " <Arr [center] <Endl < Endl;  /*  Recursive quick left half  */  Sortunit (ARR, start, center - 1  );  /*  Recursive fast right half side  */  Sortunit (ARR, center + 1  , End );}  Void  Main (){  Int N = 20 ; //  Set the length of the test array to 20      Int Arr [ 20 ] = { 0 }; //  Initialize an array      For ( Int I =0 ; I <n; I ++ ) {CIN > Arr [I];} sortunit (ARR,  0 , N- 1  );  //  View final result Showarray (ARR, 0 , N- 1  );} 

Code test:

Test data:

Use MATLAB to randomly generate a 1*20 vector in the range of (1,100 ).

> A = Randi ([1,100)

Vector:

66 4 85 94 68 76 75 40 66 18 71 4 28 5 10 83 70 32 96 4

Output: