binary search

Java implementation

public int BinarySort(int[] a, int key) {
        int left, right, mid;
        left = 0;
        right = a.length - 1;
        while (left <= right) {
            mid = (left + right) / 2;
            if (a[mid] < key)
                left = mid + 1;
            else if (a[mid] > key)
                right = mid - 1;
            else
                return mid;
        }
        return -1;
    }

Its time complexity is O(logN)