Summary: Binary Search

Iterative ways: 

 1 int binarySearch (int[] a, int x) {

 2    int low = 0;

 3    int high = a.length - 1;

 4    int mid;

 5 

 6    while (low <= high) {

 7       mid = (low + high) / 2;

 8       if (a[mid] < x) {

 9          low = mid + 1;

10       }   

11       else if (a[mid] > x) {

12          high = mid - 1;

13       }

14       else {

15          return mid;

16       } 

17    }              

18    return -1;

19 }

Recursive ways:

 1 int binarySearchRecursive (int[] a, int x, int low, int high) {

 2     if (low > high) return -1; //error

 3     

 4     int mid = (low + high) / 2;

 5     if (a[mid] < x) {

 6         return binarySearchRecursive(a, x, mid + 1, high);

 7     }

 8     else if (a[mid] > x) {

 9         return binarySearchRecursive(a, x, low, mid - 1);

10     }

11     else {

12         return mid;

13     }

14 }