Given a string s. In one step you can insert any character at any index of the string.
Return the minimum number of steps to make s palindrome.
A Palindrome String is one that reads the same backward as well as forward.
Example 1:
Input: s = "zzazz"
Output: 0
Explanation: The string "zzazz" is already palindrome we don't need any insertions.
Example 2:
Input: s = "mbadm"
Output: 2
Explanation: String can be "mbdadbm" or "mdbabdm".
Example 3:
Input: s = "leetcode"
Output: 5
Explanation: Inserting 5 characters the string becomes "leetcodocteel".
Constraints:
-
1 <= s.length <= 500 -
sconsists of lowercase English letters.
SOLUTION:
class Solution:
def minIns(self, s, i, j):
if i == j:
return 0
if i == j - 1:
if s[i] == s[j]:
return 0
return 1
if (i, j) in self.cache:
return self.cache[(i, j)]
if s[i] == s[j]:
curr = self.minIns(s, i + 1, j - 1)
self.cache[(i, j)] = curr
return curr
else:
curr = 1 + min(self.minIns(s, i + 1, j), self.minIns(s, i, j - 1))
self.cache[(i, j)] = curr
return curr
def minInsertions(self, s: str) -> int:
self.cache = {}
return self.minIns(s, 0, len(s) - 1)
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