664. Strange Printer

Problem Link

Description

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There is a strange printer with the following two special properties:

• The printer can only print a sequence of the same character each time.
• At each turn, the printer can print new characters starting from and ending at any place and will cover the original existing characters.

Given a string s, return the minimum number of turns the printer needed to print it.

 

Example 1:

Input: s = "aaabbb"
Output: 2
Explanation: Print "aaa" first and then print "bbb".

Example 2:

Input: s = "aba"
Output: 2
Explanation: Print "aaa" first and then print "b" from the second place of the string, which will cover the existing character 'a'.

 

Constraints:

• 1 <= s.length <= 100
• s consists of lowercase English letters.

Solution

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Python3

class Solution:
    def strangePrinter(self, s: str) -> int:
        s = [key for key, group in itertools.groupby(s)]
 
        @cache
        def go(i, j):
            if i == j: return 1
 
            res = inf
 
            for k in range(i, j):
                res = min(res, go(i, k) + go(k + 1, j))
            
            return res - 1 if s[i] == s[j] else res
        
        return go(0, len(s) - 1)