notes35 - Implementation void radix(unsigned int *a, int n)...

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cs 251 Radix Sort -used to sort numeric keys or keys that can be represented numerically. -it assumes that each key is represented with M bits. -sorts column by column starting with the least significant column. 1. at every step, examine the bits from right to left. 2. make sure that the keys with 0s in the column appear before the keys with 1s. sort column 0 sort column 1 sort column 2 final result 10 1 = 5 0 0 0 0 00 000 00 0 = 0 0 1 0 1 01 010 01 0 = 2 1 0 1 0 10 011 11 1 = 7 1 1 1 1 11 101 01 1 = 3 0 1 1 0 11 111 Complexity: ======== -every step takes O(n) -most steps M (number of bits) -n = # of elements to sort -total time = M * O(n) = O(M*n)
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Unformatted text preview: Implementation void radix(unsigned int *a, int n) { //allocate scratch memory unsigned int *a2 = new unsigned int[n]; assert( a2 != NULL ); int M = 8 * sizeof( unsigned int ); for (int j = 0; j < M; j++) { int J = 0; for (int k = 0; k < n; k++) { if (a[k] & (1<<i) == 0) { a2[J] = a[k]; J++; } } //copy keys with 1s to a2 for (int k = 0; k < n; k++) { if (a[k] & (1<<i) != 0) { a2[j] = a[k]; } } //copy a2 to a memcpy(a, a2, n * sizeof(unsigned int)); } } M = O(log n)...
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This note was uploaded on 02/02/2012 for the course CS 251 taught by Professor Staff during the Fall '08 term at Purdue University-West Lafayette.

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notes35 - Implementation void radix(unsigned int *a, int n)...

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