Sliding window and two pointers

Sliding window

Use when you need a contiguous subset of an array or string.

Problems to practice

• Longest substring without repeating characters
• Maximum sum subarray of fixed size
• Minimum window substring
• Fruits into baskets
• Permutation in string

Two pointers

Use when you need to scan from both ends or move indices in different directions.

Problems to practice

• Valid palindrome
• Container with most water
• Merge sorted arrays
• Remove duplicates from sorted array