medium_task.md

3. Longest Substring Without Repeating Characters

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Given a string s, the task is to find the length of the longest substring without any repeating characters.

Examples

Example 1:

Input: `s = "abcabcbb"`
Output: `3`
Explanation: The longest substring without repeating characters is "abc", which has a length of 3.

Example 2:

Input: `s = "bbbbb"`
Output: `1`
Explanation: The longest substring without repeating characters is "b", which has a length of 1.

Example 3:

Input: `s = "pwwkew"`
Output: `3`
Explanation: The longest substring without repeating characters is "wke", which has a length of 3. Note that "pwke" is not a substring as it contains repeating characters.

Constraints

• 0 <= s.length <= 5 * 10^4
• s consists of English letters, digits, symbols, and spaces.

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5. Longest Palindromic Substring

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Given a string s, return the longest palindromic substring in s.

Examples

Example 1:

Input: `s = "babad"`
Output: `"bab"`
Explanation: `"aba"` is also a valid answer.

Example 2:

Input: `s = "cbbd"`
Output: `"bb"`

Constraints

• 1 <= s.length <= 1000
• s consists of only digits and English letters.

6. Zigzag Conversion

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The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P A H N
APLSIIG
Y I R

And then read line by line: "PAHNAPLSIIGYIR"

Write the code that will take a string and make this conversion given a number of rows:

string convert(string s, int numRows);

Examples

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:
P     I    N
A   L S  I G
Y A   H R
P     I

Example 3:

Input: s = "A", numRows = 1
Output: "A"

Constraints:

1. 1 <= s.length <= 1000
2. s consists of English letters (lower-case and upper-case), ',' and '.'.
3. 1 <= numRows <= 1000