排序

二分查找：

public class BinarySearch {       public static final int NOT_FOUND = -1;       /**      * Performs the standard binary search using two comparisons per level.      *      * @return index where item is found, or NOT_FOUND.      */     public static int binarySearch(Comparable[] a, Comparable x) {         int low = 0;         int high = a.length - 1;         int mid;           while (low <= high) {             mid = (low + high) / 2;               if (a[mid].compareTo(x) < 0)                 low = mid + 1;             else if (a[mid].compareTo(x) > 0)                 high = mid - 1;             else                 return mid;         }           return NOT_FOUND; // NOT_FOUND = -1     }       // Test program     public static void main(String[] args) {         int SIZE = 8;         Comparable[] a = new Integer[SIZE];         for (int i = 0; i < SIZE; i++)             a[i] = new Integer(i * 2);           for (int i = 0; i < SIZE * 2; i++)             System.out.println("Found " + i + " at "                     + binarySearch(a, new Integer(i)));       } }

 

 

快速排序：

public class QuickSort {       public static void quickSort(int[] a, int l, int r) {         if (l < r) {             int q = partition(a, l, r);             quickSort(a, l, q - 1);             quickSort(a, q + 1, r);         }     }       public static int partition(int[] a, int l, int r) {         int pivot = a[l];         int i = l;         for (int j = l + 1; j <= r; j++) {             if (a[j] <= pivot) {                 i = i + 1;                 exchange(a, i, j);             }         }         exchange(a, l, i);         return i;       }       public static void exchange(int[] a, int i, int j) {         int tmp = a[i];         a[i] = a[j];         a[j] = tmp;     }       public static void display(int[] a) {         for (int i = 0; i < a.length; i++) {             System.out.print(a[i] + "  ");         }     }       /**      * @param args      */     public static void main(String[] args) {         int[] a = { 2, 1, 5, 3, 7, 5, 9, 0, 10, -11, 100, 20,33, 39,12,-29,-2,8 };         quickSort(a, 0, a.length-1);         display(a);     } }

 

 

归并排序：

import java.util.Random;   public class MergeSort {     private int[] L;     private int[] R;       public void sort(int[] a, int l, int r) {         int p;         if (l < r) {             p = (l + r) / 2;             sort(a, l, p);             sort(a, p + 1, r);             merge(a, l, p, r);         }     }       private void merge(int[] a, int l, int p, int r) {         int n1 = p - l + 1;         int n2 = r - p;           L = new int[n1 + 1];         R = new int[n2 + 1];           for (int i = 0; i < n1; i++) {             L[i] = a[l + i];         }           for (int j = 0; j < n2; j++) {             R[j] = a[p + 1 + j];         }           L[n1] = Integer.MAX_VALUE;         R[n2] = Integer.MAX_VALUE;           int i = 0;         int j = 0;         for (int k = l; k <= r; k++) {             if (L[i] <= R[j]) {                 a[k] = L[i];                 i++;             } else {                 a[k] = R[j];                 j++;             }         }       }       public static void main(String[] args) {         int[] arr = new int[10];         Random r = new Random();         for (int i = 0; i < 10; i++) {             arr[i] = r.nextInt(100);         }           for (int i = 0; i < 10; i++) {             System.out.print(arr[i] + " ");         }         System.out.println();         new MergeSort().sort(arr, 0, arr.length - 1);         for (int i = 0; i < 10; i++) {             System.out.print(arr[i] + " ");         }         System.out.println();     } }

  

堆排序：

public class HeapSort {       private int heapLen;       public int[] sort(int[] array) {         heapLen = array.length;         buildHeap(array); // init the heap         for (int i = array.length - 1; i > 0; i--) { // swap root and last                                                         // node, up to down             swap(array, i, 0);             heapLen--;             heapify(array, 0); // reheapify the root node from 0 to n-1         }         return array;     }       private void buildHeap(int[] array) {         for (int i = heapLen / 2; i >= 0; i--) { // down to up             heapify(array, i);         }     }       private void heapify(int[] array, int i) { // heapify tree which root is i         int left = 2 * i + 1;         int right = 2 * i + 2;         int largest = 0;         if (left < heapLen && array[left] > array[i]) {             largest = left;         } else {             largest = i;         }         if (right < heapLen && array[right] > array[largest]) {             largest = right;         }         if (largest != i) {             swap(array, i, largest);             heapify(array, largest);         }     }       private void swap(int[] array, int i, int j) {         int temp = array[i];         array[i] = array[j];         array[j] = temp;     }       public static void main(String[] args) {         int[] array = { 1, 21, 34, 79, 68, 2, 3, 8, 3,33, -2,7, 87, 32, 24, 6, 776 };         HeapSort heapSort = new HeapSort();         int[] result = heapSort.sort(array);         for (int i = 0; i < result.length; i++) {             System.out.print(result[i] + " ");         }     } }