归并排序

比较操作的次数介于(nlogn) / 2和nlogn − n + 1。 赋值操作的次数是(2nlogn)

 

nlogn − n + 1--->赋值次数-父节点个数【二叉树的父节点个数=子节点数n-1】

 

最多比较次数是两个有序数组个数和-1。

 

class ArrayUtil {private int[] tmpArray;private int[] theArray;/** * 传入需要排序的数组，进行归并排序 * @param array 需要排序的数组 */public void mergeSort(int[] array) { theArray = array;tmpArray = new int[array.length];recMergeSort(0, array.length - 1);}/** * 归并排序 * @param lowerBound 数组起始下标 * @param upperBound 数组尾下标 */private void recMergeSort(int lowerBound, int upperBound) {if (lowerBound == upperBound)return;else {int mid = (lowerBound + upperBound) / 2;recMergeSort(lowerBound, mid);recMergeSort(mid + 1, upperBound);merge(lowerBound, mid + 1, upperBound);}} /** * 合并排序数组 * @param lowPtr 数组的起始下标 * @param highPtr 数组的分界下标 * @param upperBound 数组的尾下标 */private void merge(int lowPtr, int highPtr, int upperBound) {int j = 0;int lowerBound = lowPtr;int mid = highPtr - 1;int n = upperBound - lowerBound + 1;while (lowPtr <= mid && highPtr <= upperBound) {if (theArray[lowPtr] < theArray[highPtr]) {tmpArray[j++] = theArray[lowPtr++];} else {tmpArray[j++] = theArray[highPtr++];}}while (lowPtr <= mid) {tmpArray[j++] = theArray[lowPtr++];}while (highPtr <= upperBound) {tmpArray[j++] = theArray[highPtr++];}for (j = 0; j < n; j++) {theArray[lowerBound + j] = tmpArray[j];}}}