Two-Pointers

LeetCode 763 note: record each letter’s last index, extend the current part’s end while scanning, and cut when the scan reaches it

Dummy heads, reversal (whole list, a range, half), fast and slow pointers for middles and cycles, two pointers n apart, pairwise swaps, two lists meeting, and copying a list with random pointers via a hash map

Converging pointers, one pointer per sequence, skipping blanks to compare positions, counting pairs after sorting, and the in-place write pointer

Lower / upper bound, binary search on the answer, k-th smallest, integer roots, and why the two interval styles must not be mixed

LeetCode 493 note: when the counting condition differs from the sort order, scan first, then merge

LeetCode 2426 note: simplify the inequality, then decide whether the matches form a prefix or a suffix

LeetCode 88 note: merge from the back with O(1) extra space

LeetCode 21 note: the dummy node, and why Python assignment is not a copy

LeetCode 1842 note: a palindrome is determined by its left half and the middle digit stays put; take the next permutation of the left half and mirror it

LeetCode 719 note: binary search on the distance, counting pairs with distance <= mid using a sliding window

LeetCode 2193 note: greedily fix the outer pair: take the last character and swap its leftmost partner to the front, costing that index; the unpaired character ends in the middle, costing its distance there

LeetCode 4026 note: greedily match from the left for each worker’s earliest station and from the right for the latest; splitting between workers i and i+1, the largest gap is latest[i+1] - earliest[i]