Summary: Binary Search

Iterative ways:

 int binarySearch (int[] a, int x) {
    int low = 0;
    int high = a.length - 1;
    int mid;

    while (low <= high) {
       mid = (low + high) / 2;
       if (a[mid] < x) {
          low = mid + 1;
       }
       else if (a[mid] > x) {
          high = mid - 1;
       }
       else {
          return mid;
       }
    }
    return -1;
 }

Recursive ways:

 int binarySearchRecursive (int[] a, int x, int low, int high) {
     if (low > high) return -1; //error

     int mid = (low + high) / 2;
     if (a[mid] < x) {
         return binarySearchRecursive(a, x, mid + 1, high);
     }
     else if (a[mid] > x) {
         return binarySearchRecursive(a, x, low, mid - 1);
     }
     else {
         return mid;
     }
 }