Easy

LeetCode 69 note: find the largest mid with mid² <= x; when a closed-interval search ends, r is the answer

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

LeetCode 66 note: add one from the last digit, turning 9s into 0s while carrying, and prepend 1 when every digit was 9

LeetCode 58 note: split() with no argument ignores trailing spaces; return the length of the last word

LeetCode 35 note: find the first position >= target (lower bound); a half-open [l, r) needs r = mid, not r = mid - 1

LeetCode 28 note: try matching needle at every start, or use str.find; index raises when not found

LeetCode 27 note: the write pointer copies only values not equal to val, returning how many were written

LeetCode 620 note: odd id and description not ‘boring’, ordered by rating from high to low

LeetCode 596 note: group by class with HAVING COUNT(DISTINCT student) >= 5; older test data had duplicate rows, so count distinct students

LeetCode 595 note: filter with WHERE and OR for an area of at least 3 million or a population of at least 25 million

LeetCode 197 note: self-join Weather on a one-day date difference with today warmer; compare dates with DATEDIFF, never ids

LeetCode 196 note: it must be a DELETE, not a SELECT; keep only the smallest id per email and delete the rest