Array

LeetCode 2859 note: count the set bits of the index, not of the value

LeetCode 154 note: compare with the right end as in LC 153; on equality the break could be on either side, so r -= 1, worst case O(n)

LeetCode 611 note: sort, fix the longest side k, and use two pointers for the shorter sides; when the sum is large enough every i in between works, adding j - i at once

LeetCode 540 note: before the single element every pair starts at an even index, so binary search whether nums[mid] equals nums[mid + 1] at an even mid

LeetCode 275 note: with sorted citations, find the first i where citations[i] >= n - i; the answer is n - i, in O(log n) with binary search

LeetCode 1991 note: compute the total, maintain the left sum while scanning, and get the right sum as total - left - nums[i]

LeetCode 1732 note: the altitudes are prefix sums of gain starting from 0; take the maximum

LeetCode 1480 note: the definition of a prefix sum, adding each element to the previous running total

LeetCode 1413 note: the start value plus every prefix sum must be at least 1, so it is max(1, 1 - minimum prefix sum)

LeetCode 2335 note: the answer is max(the largest count, ceil(total / 2)); simulating means filling one cup from each of the two largest every second

LeetCode 2099 note: pick the k largest values along with their indices, then sort by index to restore the original order

LeetCode 2357 note: each operation zeroes the group of the smallest positive value, so the answer is the number of distinct positive values