[알고리즘] 기수정렬

 

 

소스코드 (C++)

#include <iostream>

// Function to find the maximum number to determine the number of digits
int getMax(int arr[], int n) {
    int max = arr[0];
    for (int i = 1; i < n; i++)
        if (arr[i] > max)
            max = arr[i];
    return max;
}

// Using counting sort to sort elements based on significant places
void countingSort(int arr[], int n, int exp) {
    const int BASE = 10;
    int* output = new int[n];
    int count[BASE] = { 0 };

    // Store count of occurrences in count[]
    for (int i = 0; i < n; i++)
        count[(arr[i] / exp) % BASE]++;

    // Change count[i] so that count[i] contains the actual
    // position of this digit in output[]
    for (int i = 1; i < BASE; i++)
        count[i] += count[i - 1];

    // Build the output array
    for (int i = n - 1; i >= 0; i--) {
        output[count[(arr[i] / exp) % BASE] - 1] = arr[i];
        count[(arr[i] / exp) % BASE]--;
    }

    // Copy the output array to arr[], so that arr[] contains
    // sorted numbers according to the current digit
    for (int i = 0; i < n; i++)
        arr[i] = output[i];
}

// Radix Sort function
void radixSort(int arr[], int n) {
    // Find the maximum number to determine the number of digits
    int max = getMax(arr, n);

    // Do counting sort for every digit
    for (int exp = 1; max / exp > 0; exp *= 10)
        countingSort(arr, n, exp);
}

// Utility function to print an array
void printArray(int arr[], int n) {
    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);
    printf("\n");
}

// Driver program to test above functions
int main() {
    int arr[] = { 170, 45, 75, 90, 802, 24, 2, 66 };
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("Given array is \n");
    printArray(arr, n);

    // Perform radix sort
    radixSort(arr, n);

    printf("\nSorted array is \n");
    printArray(arr, n);

    return 0;
}

 

실행화면

Given array is 170 45 75 90 802 24 2 66 Sorted array is 2 24 45 66 75 90 170 802