programming-for-dummies

Sequential Search 413
Binary searching
A variation of block searching is binary searching, which essentially uses a
block half the size of the list. After dividing a list in half, the algorithm compares
the last value of the first half of the list. If this value is smaller than the
value it’s trying to find, the algorithm knows to search the second list instead.
Otherwise, it searches the first half of the list.
The algorithm repeatedly divides the list in half and searches only the list
that contains the range of values it’s trying to find. Eventually, the binary
search finds the data, as shown in Figure 2-4.
18 46 89 93 102 146 198
18 46 89 93 102 146 198
Figure 2-4:
Binary
searching
divides a list
in half until
it eventually
finds its
data.
93 102
93 102
146 198
Binary searching keeps dividing a list in half
until it eventually finds the data, such as finding
the number 102.
The binary search algorithm works like this:
1. Divide a sorted list in half.
2. Compare the last value of the first half of the list.
If this last value is less than the desired value, search this half of the list.
Otherwise, search the other half of the list.
3. Repeat Steps 1 and 2 until the desired value is found or confirmed not
to exist.
Book IV
Chapter 2
Searching
Algorithms