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radix_sort.cpp: Add Radix Sort Algorithm
This adds Radix sort which sorts array by sorting from lowest significant digit to highest. Closes NITSkmOS#222
Paawan Mukker
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Oct 12, 2018
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#include <iostream> | ||
#include <algorithm> | ||
#include <cmath> | ||
using namespace std; | ||
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/* | ||
Utility function for Radix sort to sort given array for dth digit. | ||
This is essentially modified version of counting sort. | ||
Parameters: | ||
int a[] - Integer array a to be sorted. | ||
int n - size of array a. | ||
int d - Digit by which to sort the array with (0 based indexing). | ||
*/ | ||
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void radix_digit_util(int a[], int n, int d) { | ||
if(a == NULL) return; | ||
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int exp = pow(10, d); | ||
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int *cnt = new int[10]; //array to store count of each occurences | ||
int *out = new int[n]; //Out array to store sorted values | ||
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// Intitialise the count array to 0 | ||
for (int i = 0; i < n; ++i) | ||
cnt[i] = 0; | ||
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// Count each occurences digit wise | ||
for (int i = 0; i < n; ++i) | ||
cnt[(a[i]/exp)%10]++; | ||
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// Cumulative count array | ||
for (int i = 1; i < n; ++i) | ||
cnt[i]+=cnt[i-1]; | ||
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// Sort | ||
for (int i = n - 1; i >= 0; i--) { | ||
// Note - starting from n-1 to maintain "stable sort" property | ||
out[cnt[(a[i]/exp)%10] - 1] = a[i]; | ||
cnt[(a[i]/exp)%10]--; | ||
} | ||
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// Copy results back to orignal array | ||
for (int i = 0; i < n; i++) | ||
a[i] = out[i]; | ||
} | ||
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/* | ||
Radix sort implementation for sorting given array assuming the base 10. | ||
Note - // Works on Non-negative integer array only. | ||
Parameters: | ||
int a[] - Non-negative Integer array a to be sorted. | ||
int n - size of array a. | ||
*/ | ||
void radix_sort(int a[], int n) { | ||
if(a == NULL) return; | ||
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// Get the iterator to max element for calculating maximum number of digits. | ||
int * max_a_itr = max_element(a, a+n); | ||
int max_a = *max_a_itr; | ||
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// Get maximum number of digits of all elements in array a | ||
int max_d = 0; | ||
while(max_a) { | ||
max_d++; | ||
max_a = max_a/10; | ||
} | ||
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// Sort the array digit wise starting from lowest significant digit to highest. | ||
for (int d = 0; d < max_d; d++) | ||
radix_digit_util(a, n, d); | ||
} | ||
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int main() { | ||
ios_base::sync_with_stdio(false); //For faster io | ||
int a[] = {1, 2, 9, 293, 41, 15, 52, 3, 121, 7, 1223, 3449, 15, 1 }; | ||
int n = sizeof(a)/sizeof(a[0]); | ||
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cout << "Input Array:\n"; | ||
for (int i = 0; i < n; i++) { | ||
cout << a[i] << " "; | ||
} | ||
cout << "\n"; | ||
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radix_sort(a, n); | ||
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cout << "Sorted Array:\n"; | ||
for (int i = 0; i < n; i++) { | ||
cout << a[i] << " "; | ||
} | ||
cout << "\n"; | ||
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return 0; | ||
} |