归并排序和快速排序的实现

来源：互联网发布：开名淘宝店是真是假编辑：程序博客网时间：2024/05/17 01:17

两种排序都是用的是divide and conquer的思想，时间复杂度都是O(nlogn).

归并排序的难点在merge部分，T(n) = 2(n/2) + n, 所以复杂度是O(nlogn)

public static void mergeSort(int[] A){if(A == null || A.length <= 1) return;mergeSort2(A, 0, A.length - 1);}private static void mergeSort2(int[] A, int start, int end){if(start < end){int mid = (start + end) / 2;mergeSort2(A, start, mid);mergeSort2(A, mid + 1, end);merge(A, start, mid, end);}}private static void merge(int[] A, int start, int mid, int end){int[] temp = new int[end - start + 1];int i = start, j = mid + 1, k = 0;while(i <= mid && j <= end){if(A[i] <= A[j]){temp[k++] = A[i++];} else {temp[k++] = A[j++];}}while(i <= mid){temp[k++] = A[i++];}while(j <= end){temp[k++] = A[j++];}for(int p = 0; p < temp.length; p++){A[start++] = temp[p];}}

public static void quickSort(int[] A){if(A == null || A.length <= 1) return;quickSort2(A, 0, A.length - 1);}private static void quickSort2(int[] A, int start, int end){if(start < end){int i = start, j = end, pivot = A[start];while(i < j){while(i < j && A[j] >= pivot){j--;}while(i < j && A[i] <= pivot){i++;}if(i < j){int temp = A[i];A[i] = A[j];A[j] = temp;}}A[start] = A[i];A[i] = pivot;quickSort2(A, start, i - 1);quickSort2(A, i + 1, end);}}

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