Two-Pointers

LeetCode 1498 note: only the minimum and maximum matter, so order does not and we can sort; fixing nums[left] as the minimum, the elements between are free, giving 2^(right - left) choices

LeetCode 1712 note: fix the first cut and find the valid range of the second cut with two bisects or two monotonic pointers

LeetCode 825 note: after sorting, the people someone can invite have ages in (0.5 × age + 7, age], a contiguous range kept with two same-direction pointers, minus the person themself

LeetCode 2200 note: extend each key k positions both ways, and keep a pointer to how far output has gone so overlapping ranges are not emitted twice

LeetCode 3794 note: one line with slicing; a hand-written two-pointer version must convert the string to a list first

LeetCode 3750 note: compare the binary string with its reverse bit by bit; the number of mismatches is the answer

LeetCode 2300 note: sort potions, bisect a threshold per spell, and compute the threshold with integer ceil to avoid float error

LeetCode 3649 note: simplify the condition to “larger absolute value <= 2 × smaller absolute value”, then count with two pointers over sorted absolute values

LeetCode 3643 note: flip only the submatrix rows, swapping the slices of rows x + i and x + k - 1 - i

Sliding window over meetings; track total duration in a k-sized window and compute free span between boundaries.

Three approaches: brute force, counting optimization, and sliding window over word-length offsets.

Sliding window with two pointers; minimize subarray length where sum ≥ target.