How hard is LeetCode 2911. Minimum Changes to Make K Semi-palindromes?

LeetCode 2911. Minimum Changes to Make K Semi-palindromes is rated Hard on LeetCode.

What is the time complexity of LeetCode 2911. Minimum Changes to Make K Semi-palindromes?

The Python solution on this page runs in O(n) (after optional sort O(n log n)).

What is the space complexity of LeetCode 2911. Minimum Changes to Make K Semi-palindromes?

The Python solution on this page uses O(1) auxiliary space.

What topics does LeetCode 2911. Minimum Changes to Make K Semi-palindromes cover?

LeetCode 2911. Minimum Changes to Make K Semi-palindromes is tagged Two Pointers, String and Dynamic Programming on LeetCode.

Minimum Changes to Make K Semi-palindromes — LeetCode 2911 Python Solution

HardTwo PointersStringDynamic Programming

Problem: #2911
Pattern: Two Pointers
Reading time: 4 min
Source: leetcode.com

The problem

Given a string s and an integer k, partition s into k substrings such that the letter changes needed to make each substring a semi-palindrome are minimized. Return the minimum number of letter changes required.

Python solution

Python

class Solution:
    def minimumChanges(self, s: str, k: int) -> int:
        n = len(s)
        g = [[inf] * (n + 1) for _ in range(n + 1)]
        for i in range(1, n + 1):
            for j in range(i, n + 1):
                m = j - i + 1
                for d in range(1, m):
                    if m % d == 0:
                        cnt = 0
                        for l in range(m):
                            r = (m // d - 1 - l // d) * d + l % d
                            if l >= r:
                                break
                            if s[i - 1 + l] != s[i - 1 + r]:
                                cnt += 1
                        g[i][j] = min(g[i][j], cnt)

        f = [[inf] * (k + 1) for _ in range(n + 1)]
        f[0][0] = 0
        for i in range(1, n + 1):
            for j in range(1, k + 1):
                for h in range(i - 1):
                    f[i][j] = min(f[i][j], f[h][j - 1] + g[h + 1][i])
        return f[n][k]

Complexity

Measure	Complexity
Time	O(n) (after optional sort O(n log n))
Space	O(1) auxiliary

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 2911. Minimum Changes to Make K Semi-palindromes is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Two Pointers.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 2911. Minimum Changes to Make K Semi-palindromes?: LeetCode 2911. Minimum Changes to Make K Semi-palindromes is rated Hard on LeetCode.
What is the time complexity of LeetCode 2911. Minimum Changes to Make K Semi-palindromes?: The Python solution on this page runs in O(n) (after optional sort O(n log n)).
What is the space complexity of LeetCode 2911. Minimum Changes to Make K Semi-palindromes?: The Python solution on this page uses O(1) auxiliary space.
What topics does LeetCode 2911. Minimum Changes to Make K Semi-palindromes cover?: LeetCode 2911. Minimum Changes to Make K Semi-palindromes is tagged Two Pointers, String and Dynamic Programming on LeetCode.