Bit-Manipulation

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

LeetCode 3688 note: OR only the even numbers; the starting value 0 is also the answer when there are none

LeetCode 3644 note: every misplaced number must be swapped, so each bit of k must belong to all of them; the answer is the AND of every misplaced number

LeetCode 2044 note: the maximum OR is the OR of everything; once backtracking reaches it, count the rest as 2^k

LeetCode 1290 note: walk head to tail, shifting the running value left by one and adding the new bit

LeetCode Problem Solving

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

LeetCode 222 note: in a complete tree, equal leftmost depths on both sides mean one side is perfect, counted as 2^h - 1, for O(log² n)

LeetCode 473 note: the total must be divisible by 4; place sticks from longest to shortest into one of four sides, skipping a side that would overflow or that equals a side already tried

LeetCode 397 note: even numbers are always halved; for odd numbers try +1 and -1 with memoized recursion, since n is too large for an n-sized array

LeetCode 338 note: dp[i] = dp[i » 1] + (i & 1), or dp[i] = dp[i - highest power of two] + 1

LeetCode 187 note: count every length-10 substring in a hash map and return those seen more than once