With a sorted data-set, we can take advantage of the ordering to make a sort which is more efficient than going element by element.
Binary search requires a sorted data-set. We then take the following steps:
We eventually run out of values in the list, or find the target value.
In each iteration, we are cutting the list in half. The time complexity is O(log N).
# In-place binary search example
def binary_search(sorted_list, left_pointer, right_pointer, target):
# this condition indicates we've reached an empty "sub-list"
if left_pointer >= right_pointer:
return "value not found"
# We calculate the middle index from the pointers now
mid_idx = (left_pointer + right_pointer) // 2
mid_val = sorted_list[mid_idx]
if mid_val == target:
return mid_idx
if mid_val > target:
# we reduce the sub-list by passing in a new right_pointer
return binary_search(sorted_list, left_pointer, mid_idx, target)
if mid_val < target:
# we reduce the sub-list by passing in a new left_pointer
return binary_search(sorted_list, mid_idx + 1, right_pointer, target)
values = [77, 80, 102, 123, 288, 300, 540]
start_of_values = 0
end_of_values = len(values)
result = binary_search(values, start_of_values, end_of_values, 288)
print("element {0} is located at index {1}".format(288, result))
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# Iterative version
def binary_search(sorted_list, target):
left_pointer = 0
right_pointer = len(sorted_list)
# fill in the condition for the while loop
while left_pointer < right_pointer:
# calculate the middle index using the two pointers
mid_idx = (right_pointer + left_pointer) // 2
mid_val = sorted_list[mid_idx]
if mid_val == target:
return mid_idx
if target < mid_val:
# set the right_pointer to the appropriate value
right_pointer = mid_idx
if target > mid_val:
# set the left_pointer to the appropriate value
left_pointer = mid_idx + 1
return "Value not in list"
# test cases
print(binary_search([5,6,7,8,9], 9))
print(binary_search([5,6,7,8,9], 10))
print(binary_search([5,6,7,8,9], 8))
print(binary_search([5,6,7,8,9], 4))
print(binary_search([5,6,7,8,9], 6))