Learn the fundamental concepts of array manipulation and hash table techniques with clear examples and code implementations.
Understanding how computer memory works and why arrays are fast
8:30Fixed-size arrays with O(1) access time
12:15Resizable arrays (ArrayList, Vector) and amortized analysis
15:45Key-value pairs with O(1) average operations
18:20How hashing works and collision handling
14:10def two_sum(nums, target):
hash_map = {} # value -> index
for i, num in enumerate(nums):
complement = target - num
if complement in hash_map:
return [hash_map[complement], i]
hash_map[num] = i
return []def count_frequency(arr):
freq = {}
for item in arr:
freq[item] = freq.get(item, 0) + 1
return freq