Two-Pointers

LeetCode 925 note: one pointer each over name and typed; every typed character either matches the next name character or repeats the previous typed character

LeetCode 922 note: pointers i over even slots and j over odd slots, each stepping by two; when slot i holds an odd number, move j to a misplaced even and swap

LeetCode 917 note: two pointers each skip non-letters and swap when both point at letters; convert the string to a list first

LeetCode 905 note: a write pointer swaps even numbers to the front, just like move zeroes

LeetCode 876 note: fast moves two steps and slow one; when fast reaches the end slow is in the middle, the right-middle for even lengths

LeetCode 844 note: simulate backspaces with a stack; for O(1) space, walk from the end and count how many characters each # skips

LeetCode 832 note: reverse each row and invert its bits, which two pointers can do at once

LeetCode 821 note: one left-to-right pass for the distance to the nearest c on the left, then a right-to-left pass taking the minimum

LeetCode 696 note: split the string into runs of equal characters; each adjacent pair of runs contributes min(previous, current) substrings

LeetCode 680 note: at the first mismatch the only options are deleting the left or the right character; check whether either remainder is a palindrome

LeetCode 653 note: traverse while keeping a set of seen values; finding k - val in it means a pair exists

LeetCode 557 note: split on spaces, reverse each word, and join with spaces