Find the Longest Palindrome in an Array using Python
Longest Palindrome in an Array
Here, in this page we will discuss the program to find the longest palindrome in an array in python programming language, we will discuss two different methods to find the longest palindromic element in the given array.
Here in this page we will discuss the following methods to find the longest palindromic number.
- Method 1 : Using Naive Approach
- Method 2 : Using Sorting
Method 1 :
- Create a function ispalindrome(int n), it will return 1 if the passing number is palindrome otherwise return 0.
- Inside the main function, create a variable say res = -1, that hold the maximum palindrome number.
- Run a loop from [0, n), and check if(ispalindrome(arr[i]) && res<arr[i]), then set res = arr[i].
- Print the value of res.
Method 1 : Code in Python
Run
# Function to check if n is palindrome
def isPalindrome(n):
divisor = 1
while (int(n / divisor) >= 10):
divisor *= 10
while (n != 0):
leading = int(n / divisor)
trailing = n % 10
if (leading != trailing):
return False
n = int((n % divisor) / 10)
divisor = int(divisor / 100)
return True
# Function to find the largest palindromic element
def largestPalindrome(arr, n):
currentMax = -1
for i in range(0, n, 1):
if (arr[i] > currentMax and isPalindrome(arr[i])):
currentMax = arr[i]
return currentMax
# Driver Code
arr = [1, 232, 5545455, 909090, 161]
n = len(arr)
# print required answer
print(largestPalindrome(arr, n))Output
5545455
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Method 2 :
In this method we first sort the array and then start traversing the array from end, and return the element that satisfy the condition, that it is palindrome.
- Sort the array using inbuilt sort() function.
- Start traversing from end of the array,
- Print the element if it is palindrome.
- If no element found then print -1.
About sort() function in Python
The sort() method is a built-in Python method that, by default, sorts the list in ascending order.However, you can modify the order from ascending to descending by specifying the sorting criteria.
array_name.sort(reverse=True|False, key=myFunc) , this will sort the array in descending order.
Method 2 : Code in Python
Run
# Function to check if n is palindrome
def isPalindrome(n):
divisor = 1
while (int(n / divisor) >= 10):
divisor *= 10
while (n != 0):
leading = int(n / divisor)
trailing = n % 10
if (leading != trailing):
return False
n = int((n % divisor) / 10)
divisor = int(divisor / 100)
return True
# Function to find the largest palindromic element
def largestPalindrome(A, n) :
# Sort the array
A.sort()
for i in range(n - 1, -1, -1) :
# If number is palindrome
if (isPalindrome(A[i])) :
return A[i]
# If no palindromic number found
return -1
# Driver Code
arr = [1, 232, 5545455, 909090, 161]
n = len(arr)
# print required answer
print(largestPalindrome(arr, n))Output
5545455
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arr=[33,44,2002,9823,8930,3980,3]
temp=[]
for i in range(len(arr)):
if str(arr[i])==str(arr[i])[::-1]:
k=len(str(arr[i]))
temp+=[int(k)]
print(max(temp))
def longpali(n,l):
out = []
for i in l:
if str(i) == str(i)[::-1]:
out.append(i)
out.sort()
return [out[-1]]
print(longpali(4,[1, 232, 5545455, 909090, 161]))
arr=list(map(int,input().split(‘,’)))
p=[]
for num in arr:
if str(num)[::-1]== str(num):
p.append(str(num))
if p:
longest_palindrome= max(p)
print(longest_palindrome)
else:
print(‘No Palindrome found.’)
lis = [101,121,3231]
lis2= []
for i in lis:
rev = 0
temp = i
while i>0:
rem = i%10
i//=10
rev = rev*10+rem
if temp == rev:
lis2.append(rev)
print(max(lis2))
less time consuming code
arr = [1, 232, 5545455, 909090, 161]
def isPali(number):
flag=le=i=0
c_n = number
orignal = c_n
# print(c_n)
while(c_n>0):
num = c_n%10
i =i*10+num
c_n=c_n//10
le+=1
if i==orignal:
flag=1
else:
flag=0
return flag, le
length=long_n=0
for i in range(0, len(arr)):
flag=isPali(arr[i])
if flag[0]==1 and flag[1]>length:
length=flag[1]
long_n+=arr[i]
print(long_n)
def checking(i,rem=0,sum=0):
save=i
while i!=0:
rem=i%10
sum=sum*10+rem
i=i//10
if save==sum:
return save
else:
return 0
palin=[]
arr = [1, 232, 5545455, 909090, 161]
for i in (arr):
palin.append(checking(i))
max=palin[0]
for i in range(1,len(palin)):
for j in range(i+1):
if palin[j]>palin[i]:
max=palin[j]
print(max)
ls=[1, 232, 5545455, 909090, 161]
ls2=[]
for num in ls:
temp=str(num)
check=”
if len(str(num))==1:
ls2.append(str(num))
else:
while num > 0:
rem = int(num)%10
check+=str(rem)
num = int(num)//10
if check==temp:
ls2.append(check)
print(f”Filtered List:{ls2}”)
print(max(ls2,key=len))
def is_palindrome(s):
n = len(s)
for i in range(n/2):
if s[i] != s[n-i-1]:
return False
return True
def find_longest_palindrome(arr):
longest_palindrome = []
for number in arr:
num_arr = [int(digit) for digit in str(number)]
if is_palindrome and len(num_arr) > len(longest_palindrome):
longest_palindrome = num_arr
return int(”.join(map(str,longest_palindrome)))
arr = [121, 12321, 45654, 67876, 987789, 22, 999]
longest_palindrome = find_longest_palindrome(arr)
print(f”longest palindrome :{longest_palindrome}”)
simple method
logic : use slice method here
code:
a =[123,1121211,2002,731,4000]
b =[]
for num in a:
c=int(str(num)[: :-1])
if num == c:
b.append(len(str(num)))
if b:
print(max(b))
else:
print(‘palidrome is not found’)
def is_int_value_palendrom(num):
original=num
reversed=0
while num>0:
last_digit=num%10
reversed=reversed*10+last_digit
num=num//10
return original==reversed
print(is_int_value_palendrom(121))
print(is_int_value_palendrom(12321))
print(is_int_value_palendrom(12345))
print(is_int_value_palendrom(-121))
print(is_int_value_palendrom(555554444411111))
def is_palendrom(num):
num=str(num)
i=0
j=len(num)-1
while i<=j:
if num[i]==num[j]:
i+=1
j-=1
else:
return False
return True
def longest_palendrom(array):
ans=dict()
for i in array:
if is_palendrom(i):
ans[i]=len(str(i))
my_sorted_dict=dict(sorted(ans.items(), key=lambda item: item[1], reverse=True))
longest_palindrome_number = list(my_sorted_dict.keys())[0]
return longest_palindrome_number
ans=longest_palendrom([1, 232, 5545455, 909090, 161])
print(ans)