CODEWITHSUNDEEP
pythonbinary-search
user5473706
user5473706

Reputation: 29

Binary Searching

I have this list called countries.txt that list all the countries by their name, area(in km2), population (eg. ["Afghanistan",647500.0,25500100]).

def readCountries(filename):
    result=[]
    lines=open(filename)

    for line in lines:
        result.append(line.strip('\n').split(',\t'))
    for sublist in result:
        sublist[1]=float(sublist[1])
        sublist[2]=int(sublist[2])

This takes in the list and prints it out. I want to creates a binary search and search through the list and print the country's information if found. With this code it should do this

printCountry("Canada") Canada, Area: 9976140.0, Population: 35295770

printCountry("Winterfell") I'm sorry, could not find Winterfell in the country list.

But it prints I'm sorry, could not find Canada in the country list 4 times then prints Canadas information.

What is going on? 

def printCountry(country):

    myList=readCountries('countries.txt')
    start = 0
    end = len(myList)-1
    while start<=end:
        mid =(start + end) / 2
        if myList[mid][0] == country:
            return '%s, Area: %.3f, Population: %i' %(country,myList[mid][1],myList[mid][2])
        elif myList[mid][0] > country:
            end = mid - 1
        else:
            start = mid + 1
        print "I'm sorry, could not find %s in the country list" %(country)

Upvotes: 0

Views: 101

Answers (2)

Michel
Michel

Reputation: 56

You have to move your unsuccessful message after the while loop and check if start > end (that means that the country was not found):

myList = readCountries('countries.txt')
start = 0
end = len(myList) - 1
while start<=end:
    mid = (start + end) / 2
    if myList[mid][0] == country:
        return '%s, Area: %.3f, Population: %i' %(country,myList[mid][1],myList[mid][2])
    elif myList[mid][0] > country:
        end = mid - 1
    else:
        start = mid + 1
if start > end:
    print "I'm sorry, could not find %s in the country list" %(country)

Upvotes: 1

Vikash Singh
Vikash Singh

Reputation: 14001

The last line 

print "I'm sorry, could not find %s in the country list" %(country)

should be outside the while loop. Also make sure the loop completed without finding the key in the file, then only you will be sure that the country name does not exist in the list.

# If condition taken from Michel's answer.
if start > end:
    print "I'm sorry, could not find %s in the country list" %(country)

Upvotes: 1

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