排序算法之归并排序
归并排序原理即将两个有序的数组合并成一个,归并排序有两种方法:递归和循环。
/*递归方法*/
void Merge(int TR1[], int TR2[], int low, int mid, int high) {//将TR2归并入TR1中 int pos1 = low; int pos2 = mid + 1; for (int i = low; i <= high; ++i) { if (pos1 <= mid && pos2 <= high) { if (TR2[pos1]>TR2[pos2]) { TR1[i] = TR2[pos2]; pos2++; } else { TR1[i] = TR2[pos1]; pos1++; } } else if (pos1<=mid) { TR1[i] = TR2[pos1++]; } else { TR1[i] = TR2[pos2++]; } } } void Msort(int SR[],int TR1[], int low, int high) { int TR2[MAXSIZE + 1]; if (low < high) {//先所有存放到TR2中,再由TR2归并到TR1 int mid = (low + high) / 2; Msort(SR,TR2,low, mid); Msort(SR,TR2,mid + 1, high); Merge(TR1, TR2, low, mid, high); } else { TR1[low] = SR[low]; } } void MergeSort1(SqList* list) { Msort(list->data,list->data,0,list->length-1); }
/*循环方法*/ void MergePass(int TR[], int SR[], int k, int length) { int i = 0; while (i <= length-2*k+1) {//两两合并 Merge(TR, SR, i, i + k-1, i + 2 * k - 1); i = i + 2 * k; } if (i <= length - k + 1) {//说明后面还剩两个子数组,一个是完整的k个,还有一个小于k Merge(TR, SR, i, i + k - 1, length); } else {//最后仅仅剩一个子数组, for (int j = i; j <= length; j++) { TR[j] = SR[j]; } } } void MergeSort2(SqList* list) {/*从最小的序列開始归并,直至完毕归并*/ int* TR = new int[list->length]; int k = 1; while (k < list->length) {//两次转存。先从data转存到TR,再从TR转存到data; MergePass(TR, list->data, k, list->length - 1); k = k * 2; MergePass(list->data, TR, k, list->length - 1); k = k * 2; } }