51 lines
1.6 KiB
Plaintext
51 lines
1.6 KiB
Plaintext
== Merge Sort ==
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Stats::
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:: Worst Case Performance: O(n log n)
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:: Best Case Performance: O(n log n)
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=== Algorithm ===
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* Conceptually, a merge sort works as follows:
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# Divide the unsorted list into n sublists, each containing 1 element (a list of 1 element is considered sorted).
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# Repeatedly merge sublists to produce new sorted sublists until there is only 1 sublist remaining. This will be the sorted list.
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=== Psuedocode ===
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{{{
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/* Array A[] has the items to sort; array B[] is a work array */
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function BottomUpSort(int n, int A[], int B[]) {
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int width;
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/* Each 1-element run in A is already "sorted". */
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/* Make successively longer sorted runs of length 2, 4, 8, 16... until whole array is sorted. */
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for(width = 1; width < n; width = 2 * width) {
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int i;
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/* Array A is full of runs of length width. */
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for(i = 0; i < n; i = i + 2 * width) {
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/* Merge two runs: A[i:i+width-1] and A[i+width:i+2*width-1] to B[] */
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/* or copy A[i:n-1] to B[] ( if(i+width >= n) ) */
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BottomUpMerge(A, i, min(i+width, n), min(i+2*width, n), B);
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}
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}
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}
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BottomUpMerge(int A[], int iLeft, int iRight, int iEnd, int B[]) {
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int i0 = iLeft;
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int i1 = iRight;
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int j;
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/* While there are elements in the left or right lists */
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for(j = iLeft; j < iEnd; j++) {
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/* If left list head exists and is <= existing right list head */
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if(i0 < iRight && (i1 >= iEnd || A[i0] <= A[i1])) {
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B[j] = A[i0];
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i0 = i0 + 1;
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} else {
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B[j] = A[i1];
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i1 = i1 + 1;
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}
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}
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}
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}}}
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=== Additional Info ===
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Wikipedia Article [http://en.wikipedia.org/wiki/Merge_Sort]
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