Hash-Table

LeetCode 160 note: each pointer walks its own list then the other’s; both cover lenA + lenB steps and reach the intersection, or None, together

LeetCode 141 note: Floyd’s cycle detection, fast two steps and slow one; with a cycle they must meet, each advancing from its own position

LeetCode 13 note: add each symbol’s value left to right, subtracting instead when it is smaller than the symbol to its right

LeetCode 1 note: store seen numbers in a hash map while scanning and look up target - x; checking before storing prevents using one element twice