LeetCode

LeetCode 349 note: convert both arrays to sets and intersect them

LeetCode 345 note: the same two pointers as LC 917, with the condition switched to “is a vowel” (both cases)

LeetCode 344 note: swap with two pointers and move inward to reverse in place

LeetCode 342 note: confirm a power of two, then that the single 1 sits at an even position: n & 0x55555555 != 0, or n % 3 == 1

LeetCode 326 note: divide by 3 while possible and check for 1; without loops, n is a power of three exactly when it divides 3^19

LeetCode 292 note: whoever faces a multiple of 4 stones loses, so the first player wins when n % 4 != 0

LeetCode 290 note: pattern characters and words must correspond one to one; use two dicts or compare set sizes

LeetCode 283 note: the write pointer advances only on non-zero values, swapping with them, which pushes zeros to the back

LeetCode 278 note: find the first version where isBadVersion is True with a lower-bound binary search, calling the API O(log n) times

LeetCode 268 note: the sum of 0..n minus the array’s sum is the missing number, which may be 0

LeetCode 263 note: only positive numbers can be ugly; divide out every factor 2, 3 and 5 and check whether 1 remains

LeetCode 258 note: sum the digits repeatedly until one remains; the O(1) answer is the digital root 1 + (n - 1) % 9