Question

我被要求排序并搜索数组。排序数组很简单，我的代码工作，但每当我尝试调用二进制搜索方法时，它适用于数组中的第一个元素，但结果给我“-1”

我的完整代码如下：

 public static void main(String[] args) {

    int[] array = new int[5];
    array[0] = 50;
    array[1] = 40;
    array[2] = 10;
    array[3] = 20;
    array[4] = 100;

sort(array, (array.length - 1));

      for (int x = 0; x < array.length; x++) {
        System.out.println(" " + array[x]);
    }
    System.out.println("");
    System.out.println("Binary search (R): " + rBsearch(array, 0, (array.length), 20));
}
    public static void sort(int[] a, int last) {
    if (last > 0) {
        int max = findMax(a, last);
        swap(a, last, max);
        sort(a, last - 1);
    }
}

public static int rBsearch(int[] L, int low, int high, int k) {


    int mid = (low + high) / 2;

    if (low > high) {
        return -1;
    } else if (L[mid] == k) {
        return mid;
    } else if (L[mid] < k) {
        return rBsearch(L, k, mid + 1, high);
    } else {
        return rBsearch(L, k, low, mid - 1);
    }
 }

public static int findMax(int[] arr, int last) {

    int max = 0;
    for (int i = 0; i <= last; i++) {
        if (arr[i] > arr[max]) {
            max = i;
        }
    }
    return max;
    }

public static void swap(int[] arr, int last, int max) {
    int temp = arr[last];
    arr[last] = arr[max];
    arr[max] = temp;
}

Answer 1

你搞砸了二进制搜索间隔

public static int rBsearch(int[] L, int low, int high, int k) {


    int mid = (low + high) / 2;

    if (low > high) {
        return -1;
    } else if (L[mid] == k) {
        return L[mid];
    } else if (L[mid] < k) {
        return rBsearch(L, mid + 1, high, k);
    } else {
        return rBsearch(L, low, mid - 1, k);
    }
 }

Answer 2

在以下行中调用rBsearch方法时出错了而不是

else if (L[mid] < k) {
        return rBsearch(L, k, mid + 1, high); 
    } else {
        return rBsearch(L, k, low, mid - 1);
    }

你应该使用

else if (L[mid] < k) {
            return rBsearch(L,  mid + 1, high,k); //the order of the parameters
        } else {
            return rBsearch(L, low, mid - 1,k);
        }

Answer 3

最简单的方法是：将数组转换为列表：Arrays.asList(array)

排序：Collections#sort

搜索：Collections#binarySearch

请参阅this

Answer 4

Take Array From User
Sort Array using Build-in Function of Java...

then Search Element using Binary Search....

    import java.lang.reflect.Array;
    import java.util.Arrays;
    import java.util.Scanner;

    class BinarySearch
    {
       public static void main(String args[])
       {
          int array[];

          Scanner input = new Scanner(System.in);
          System.out.println("Enter number of elements:");
         int Size_Of_Array = input.nextInt(); 


          array = new int[Size_Of_Array];

          System.out.println("Enter " + Size_Of_Array + " integers");

          for (int counter = 0; counter < Size_Of_Array; counter++)
              array[counter] = input.nextInt();

          Arrays.sort(array);
          System.out.println("Sorting Array is :-");
          for (int counter = 0; counter < Size_Of_Array; counter++)
              System.out.println(array[counter]);

          System.out.println("Enter the search value:");
          int  Searching_item = input.nextInt();

          int First_Index=0;
          int Last_Index=Size_Of_Array-1;
          int Middle_Index=(First_Index+Last_Index)/2;

          while(First_Index <= Last_Index)
          {
              if(array[Middle_Index] < Searching_item)
              {
                  First_Index=Middle_Index+1;
              }
              else if ( array[Middle_Index] == Searching_item ) 
              {
                System.out.println(Searching_item + " found at location " + (Middle_Index + 1) + ".");
                break;
              }
              else
              {
                  Last_Index = Middle_Index - 1;
              }
              Middle_Index = (First_Index + Last_Index)/2;

              if ( First_Index > Last_Index )
              {
                  System.out.println(Searching_item + " is not found.\n");
              }
          }
        }
    }

Result of BinarySearch

使用Java进行排序和二进制搜索

4 个答案: