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 }