// File: mergesort.C // Merge Sort Routines #include #include #include #include "array.h" #include "sorts.h" // Local function prototypes // static void merge(Array&, int, int, int, int, Array&) ; static void RecMergeSort(Array&, int, int) ; static void merge( Array &A, int low1, int high1, int low2, int high2, Array &temp ) { int t=0, i1=low1, i2=low2 ; // Sanity check assert(low2 == high1 + 1) ; // while there are elements in both halves, copy the lowest one // while (i1 <= high1 && i2 <= high2) { if (A[i1] < A[i2]) { temp[t++] = A[i1++] ; } else { temp[t++] = A[i2++] ; } } // copy any remaining elements, if any // while (i1 <= high1) { temp[t++] = A[i1++] ; } while (i2 <= high2) { temp[t++] = A[i2++] ; } // copy the now-sorted elements back into the original array // for (t = low1; t <= high2; t++) { A[t] = temp[t - low1] ; } } static void RecMergeSort(Array &A, int low, int high, Array& temp) { #ifndef NDEBUG cout << "MergeSort: low = " << low << ", high = " << high << endl ; #endif if (low >= high) return ; int mid = (low + high)/2 ; RecMergeSort(A, low, mid, temp) ; RecMergeSort(A, mid + 1, high, temp) ; merge(A, low, mid, mid + 1, high, temp) ; } void MergeSort(Array& A) { Array temp(A.length()) ; RecMergeSort(A, 0, A.length()-1, temp) ; }