LeetCode Top Interview 150 - Hashmap

When tackling LeetCode problems that involve hashmaps, here are some general techniques that can be quite effective:

1. Frequency Counting: Use a hashmap to count the occurrences of elements in an array or string. This is particularly useful for problems that require you to find duplicates, the most frequent element, or to check for anagrams.

2. Two-Pointer Technique with Hashmap: In problems where you need to find pairs or triplets that meet certain criteria, you can use a hashmap to store previously seen elements while iterating through the array. This allows for efficient lookups.

3. Storing Indices: When you need to find the first or last occurrence of an element, or when you need to track the positions of elements, store the indices in the hashmap. This is useful for problems like "two-sum" where you need to find pairs of indices.

4. Sliding Window with Hashmap