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67 lines
1.9 KiB
Plaintext
67 lines
1.9 KiB
Plaintext
---
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title: '424. Longest Repeating Character Replacement'
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description: You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times
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icon: dot
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topics:
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- { name: "Hash Table", slug: "hash-table" }
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- { name: "String", slug: "string" }
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- { name: "Sliding Window", slug: "sliding-window" }
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video: "gqXU1UyA8pk"
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sidebar:
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label: 'Longest Repeating Character Replacement'
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badge: 'Medium'
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---
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### Example 1:
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- Input: `s = "ABAB", k = 2`
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- Output: `4`
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- Explanation: Replace the two 'A's with two 'B's or vice versa.
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### Example 2:
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- Input: `s = "AABABBA", k = 1`
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- Output: `4`
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- Explanation: Replace the one 'A' in the middle with 'B' and form "AABBBBA". The substring "BBBB" has the longest repeating letters, which is `4`. There may exists other ways to achieve this answer too.
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### Constraints:
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- `1 <= s.length <= 10^5`
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- `s` consists of only uppercase English letters.
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- `0 <= k <= s.length`
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## Approach
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```mermaid
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flowchart TD
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S(["characterReplacement(s, k)"]) --> I["count = {}, res = 0, l = 0, maxF = 0"]
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I --> L{"more (r, c) in s?"}
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L -- no --> E(["return res"])
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L -- yes --> A["count[c] += 1; maxF = max(maxF, count[c])"]
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A --> W{"(r - l + 1) - maxF > k? — too many chars to replace"}
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W -- yes --> P["count[s[l]] -= 1; l += 1 — shrink from the left"]
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P --> W
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W -- no --> M["res = max(res, r - l + 1)"]
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M --> L
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```
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## Solution
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```py
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class Solution:
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def characterReplacement(self, s: str, k: int) -> int:
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count = {}
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res = 0
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l = 0
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maxF = 0
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for r, c in enumerate(s):
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count[c] = 1 + count.get(c, 0)
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maxF = max(maxF, count[c])
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while (r - l + 1) - maxF > k:
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count[s[l]] -= 1
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l += 1
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res = max(res, r - l + 1)
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return res
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```
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