# Program to find minimum number of characters to be added to make it palindrome in Python

PythonServer Side ProgrammingProgramming

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Suppose we have a string s, we have to find the minimum number of characters to be inserted after s to make it a palindrome.

So, if the input is like s = "mad", then the output will be 2, as we can add "am" to make it "madam".

To solve this, we will follow these steps −

• b := 256, m := 10^9 + 7

• s := a list by taking the difference of (ASCII of i) − 97 for each i in s

• r := last element of s, l := last element of s

• n := size of s

• res := n − 1

• p := b

• for i in range n − 2 to 0, decrease by 1, do

• r := r + s[i] * p, r := r mod m

• l := l * b, l := l + s[i]

• l := l mod m

• p := p * b, p := p mod m

• if l is same as r, then

• res := i

• return res

Let us see the following implementation to get better understanding −

## Example

Live Demo

class Solution:
def solve(self, s):
b = 256
m = 10 ** 9 + 7
s = list(ord(i) − 97 for i in s)
r = l = s[−1]
n = len(s)
res = n − 1
p = b
for i in range(n − 2, −1, −1):
r += s[i] * p
r %= m
l *= b
l += s[i]
l %= m
p *= b
p %= m
if l == r:
res = i
return res
ob = Solution()
print(ob.solve(s))
"mad"
2