CODEWITHSUNDEEP
pythonwhile-loopbinary-search
Guido van Rossum
Guido van Rossum

Reputation: 3

Why my logic is not working for Binary search program?

I'm trying to create my Binary Search program using Python. But every time i get stuck with while loop. It looks i need to put break for every condition. But it'd would create a mess for my whole logic.

Kindly help me, How to get rid of such situations:

print("Enter your number of elements:")
num = int(input())

array = []

print("Enter your %d elements" %num)
for c in range(0, num):
    arrayNum = int(input())

    #Use "append" concept under array into python.
    array.append(arrayNum)

print("Enter a value which you want to find: ")
search = int(input())

first = int(0)

last = int(num-1)

middle = int((first + last)/2)

while first <= last:
    if array[middle] < search:
        first = int(middle+1)

    elif array[middle] == search:
        break
        print("%d is found at location" % search, (middle+1))

    else:
        last = int(middle-1)
        middle = int((first+last)/2)

if first > last:
    print("%d is not present in list"%search)

When i run my program, It looks while loop is still running. Please help me.

HELP WOULD BE APPRECIATED!

Upvotes: 0

Views: 55

Answers (1)

Anand S Kumar
Anand S Kumar

Reputation: 90899

Three potential issues -

  1. Binary search only works on sorted lists, you may not be entering sorted list . To make sure that the list is sorted before starting binary search do -

    array.sort()

    Do this before starting binary search while loop.

  2. Your print statement is after the break, you should put it before break, otherwise it will not get executed.

  3. Your recalculation of middle is inside the else block, but you need to recalculate middle for the case of array[middle] < search as well, a better solution would be to put that recalculation outside the else block, directly inside the while block.

Example - 

while first <= last:
    if array[middle] < search:
        first = int(middle+1)
    elif array[middle] == search:
        print("%d is found at location" % search, (middle+1))
        break
    else:
        last = int(middle-1)
    middle = int((first+last)/2)

Upvotes: 2

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