Introduction to algorithms CLRS algorithm C ++ (6) P100 base sorting

Chapter 8 linear time sorting

8.3 base sorting

In the introduction to algorithms, there are only two rows to describe the algorithm for base sorting... Let's just say something more...

Radix-sort (a, d)

1 for i ← 1 to d2     do use a stable sort to sort array A on digit i

C ++ code

1 # include <iostream> 2 3 using namespace STD; 4 5 // calculate the maximum number of digits in the array. 6 int maxdigit (int * arr, int digit) 7 {8 int n = 0; 9 int * temp = new int [digit]; 10 for (INT I = 0; I <digit; I ++) 11 temp [I] = arr [I]; 12 for (INT I = 0; I <digit; I ++) 13 {14 int counter = 1; 15 while (temp [I]/10> 0) 16 {17 counter ++; 18 temp [I]/= 10; 19} 20 if (n <counter) 21 N = counter; 22} 23 Delete [] temp; 24 return N; 25} 26 27 // base sorting 28 void radixsort (int * arr, int digit) 29 {30 int n = maxdigit (ARR, digit); 31 int * temp = new int [digit]; 32 int * COUNT = new int [10]; 33 int I, j, k; 34 int Radix = 1; 35 for (I = 1; I <= N; I ++) 36 {37 for (j = 0; j <10; j ++) 38 count [J] = 0; 39 for (j = 0; j <digit; j ++) 40 {41 K = (ARR [J]/Radix) % 10; 42 count [k] ++; 43} 44 for (j = 1; j <10; j ++) 45 count [J] = count [J-1] + Count [J]; 46 for (j = digit-1; j> = 0; j --) 47 {48 k = (ARR [J]/Radix) % 10; 49 count [k] --; 50 temp [count [k] = arr [J]; 51} 52 for (j = 0; j <digit; j ++) 53 arr [J] = temp [J]; 54 Radix * = 10; 55} 56 Delete [] temp; 57 Delete [] count; 58} 59 60 int main () 61 {62 int A [] = {22, 34, 95, 87, 56,980, 12, 48}; 63 radixsort (A, 8); 64 for (INT I = 0; I <8; I ++) 65 {66 cout <A [I] <"; 67} 68 cout <Endl; 69 return 0; 70}

In the C ++ implementation, I used an auxiliary function int maxdigit (int * arr, int digit) to calculate the maximum number of digits in the array to be sorted, in order to make the program have a larger scope of application, do not need to be sorted with the same number of digits.

The base sorting algorithm is intuitive. In an array, each element has a D-digit number, of which 1st is the nth bit, and D is the highest bit. Judge the order of each position in sequence. Base sorting requires the assistance of another stable Sorting Algorithm (stable sort.