java - 使用 Java 进行排序和二分搜索

Question

我被要求对数组进行排序和搜索。对数组进行排序很简单，我的代码也有效，但每当我尝试调用二分搜索方法时，它都会对数组中的第一个元素起作用，但结果会给出“-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

你弄乱了二分搜索间隔

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);
    }
 }