Bit-Manipulation

LeetCode 405 note: add 2^32 to a negative number to get its two’s complement, then take 4 bits at a time (% 16); handle 0 separately

LeetCode 389 note: t has one extra character; XOR every character of both strings, pairs cancel, and the extra one remains

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 231 note: a power of two has exactly one set bit, and n & (n - 1) clears the lowest one, so the result is 0 exactly then; n must be positive

LeetCode 136 note: x ^ x = 0 and x ^ 0 = x, so XOR everything; pairs cancel and the single number remains

LeetCode 67 note: add from the ends of both strings digit by digit, with carry sum // 2 and digit sum % 2