Scarl Scarl - 3 months ago 15
Java Question

Sorting and Binary search using Java

I was asked to sort and search an array. The sorting the array was simple and my code worked but then whenever I try to call the binary search method it works for the first element in the array but gives me "-1" as a result

My full code is as follows:

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

You goofed up the binary search intervals

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);
    }
 }