Number of Substrings Containing All Three Characters | LeetCode 1358 - Python

The sliding window technique efficiently solves the problem of counting substrings containing all three characters (A, B, C) by maintaining a frequency map of characters in the current window and using two pointers (left and right) to expand and contract the window while tracking valid substrings, achieving O(n) time complexity instead of the O(n²) brute force approach.