2. Problem: Longest Substring Without Repeating Characters

Category: Sliding Window, Hashing

Trick: Use two pointers with a sliding window and hash set for O(n).

Problem Description:

Given a string, find the length of the longest substring without repeating characters.

Solution:

def length_of_longest_substring(s):
    char_set = set()
    l, res = 0, 0    for r in range(len(s)):
        while s[r] in char_set:
            char_set.remove(s[l])
            l += 1        char_set.add(s[r])
        res = max(res, r - l + 1)
    return res

• Time Complexity: O(n)
• Space Complexity: O(min(n, m)) (n is string length, m is character set size)

Explanation:

Use a sliding window approach with two pointers. Expand the window with the right pointer and shrink it when encountering a repeating character.

3. Problem: Container With Most Water

Category: Two Pointers

Trick: Maximize area by shrinking the pointer with a smaller height.

Problem Description:

Given n non-negative integers representing heights, find two lines that together with the x-axis form a container that holds the most water.

Solution:

def max_area(height):
    l, r = 0, len(height) - 1    max_area = 0    while l < r:
        max_area = max(max_area, (r - l) * min(height[l], height[r]))
        if height[l] < height[r]:
            l += 1        else:
            r -= 1    return max_area

• Time Complexity: O(n)