diff --git a/TestBinarySearch2 b/TestBinarySearch2 new file mode 100644 index 00000000..2ec3ded3 --- /dev/null +++ b/TestBinarySearch2 @@ -0,0 +1,73 @@ +public class BinarySearch { + + /** + * Searches an element {@param n} in a sorted array {@param a} + * and returns its index in O(log n) time. The Index may not + * correspond to the first occurrence of the element. + * + * @param a sorted array to be searched + * @param n number to be searched in the array + * @return index of {@param n} or {@code -1} if not present + */ + public static int binarySearch(int[] a, int n) { + return binarySearch(a, n, 0, a.length - 1); + } + + public static int binarySearch(int[] a, int n, int low, int high) { + + if (low <= high) { + int mid = (low + high) / 2; // to prevent overflow you can instead do: mid = low + (high - low) / 2 + + if (n == a[mid]) { + return mid; + } else if (n < a[mid]) { + return binarySearch(a, n, 0, mid - 1); + } else { + return binarySearch(a, n, mid + 1, high); + } + } else { + return -1; + } + } + + /** + * Non-recursive version of binary search. + * + * @param a sorted array to be searched + * @param n number to be searched in the array + * @return index of {@param n} or {@code -1} if not present + */ + public static int binarySearchNonRecursive(int[] a, int n) { + int low = 0, high = a.length, mid; + while (low <= high) { + mid = (low + high) / 2; // to prevent overflow you can instead do: mid = low + (high - low) / 2 + if (n == a[mid]) { + return mid; + } else if (n < a[mid]) { + high = mid - 1; + } else { + low = mid + 1; + } + } + return -1; + } + + /** + * Driver for testing. + * + * @param a + */ + public static void main(String[] args) { + System.out.println(binarySearch(new int[]{0, 2}, 2)); + System.out.println(binarySearch(new int[]{0, 1, 2, 3}, 2)); + System.out.println(binarySearch(new int[]{0, 1, 2, 3}, 3)); + System.out.println(binarySearch(new int[]{0, 2}, 0)); + System.out.println(binarySearch(new int[]{0, 1, 2, 2, 2, 3, 3}, 2)); // doesn't return index of first occurrence + System.out.println("---------"); + System.out.println(binarySearchNonRecursive(new int[]{0, 2}, 2)); + System.out.println(binarySearchNonRecursive(new int[]{0, 1, 2, 3}, 2)); + System.out.println(binarySearchNonRecursive(new int[]{0, 1, 2, 3}, 3)); + System.out.println(binarySearchNonRecursive(new int[]{0, 2}, 0)); + System.out.println(binarySearchNonRecursive(new int[]{0, 1, 2, 2, 2, 3, 3}, 2)); + } +}