Java Source Code Analysis (1): Binary lookup + cyclic recursive implementation

Source

Source Address

    public static int binarySearch(int[] a, int key) {        return binarySearch0(a, 0, a.length, key);    }    public static int binarySearch(int[] a, int fromIndex, int toIndex,                                   int key) {        rangeCheck(a.length, fromIndex, toIndex);        return binarySearch0(a, fromIndex, toIndex, key);    }    // Like public version, but without range checks.    private static int binarySearch0(int[] a, int fromIndex, int toIndex,                                     int key) {        int low = fromIndex;        int high = toIndex - 1;        while (low <= high) {            int mid = (low + high) >>> 1;            int midVal = a[mid];            if (midVal < key)                low = mid + 1;            else if (midVal > key)                high = mid - 1;            else                return mid; // key found        }        return -(low + 1);  // key not found.    }

Thinking

Why is mid + 1, mid-1 on a subscript feel not bad ah.

Answer: After debugging and then recall, found that there is no difference, the final collapse to low = = high when all can be calculated, will not miss.

Code of your own hand

public class Source1_binarysearch {public static int binarysearch (int[] A, int fromIndex, int toindex, int key) {        int low = FromIndex;        int high = toIndex-1;            while (low <= high) {int mid = (low + high) >> 1;            int midvalue = A[mid];            Less than lo points to the middle, greater than hi to the middle, equals directly to return if (Midvalue < key) Low = mid + 1;            else if (Midvalue > key) high = mid-1;        else return mid;    } return-1;        } public static int binarysearch_recursive (int[] A, int fromIndex, int. toindex, int key) {int low = FromIndex;        int high = toIndex-1;        int result =-1;            if (low <=) {int mid = (low + high) >>> 1;            int midvalue = A[mid];            if (Midvalue < key) result = Binarysearch_recursive (a,mid +1,high + 1,key); else if (Midvalue > key) result = BinarYsearch_recursive (A,low,mid + 1-1,key);        else return mid;    } return result;        public static void Main (string[] args) {int[] a = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};        int index = binarysearch_recursive (A, 0, a.length, 11);    SYSTEM.OUT.PRINTLN (index); }}

Java source Code Analysis (1): Binary lookup + cyclic recursive implementation