Medium

LeetCode 71 note: split on /, skip empty pieces and ., pop on .. (never above root), push other names, and join with /

LeetCode 61 note: count the length and close a ring, take k %= n, walk n - k - 1 steps from the head to the new tail, and break there

LeetCode 59 note: keep four boundaries as in LC 54, but fill in 1 to n² instead of reading

LeetCode 57 note: split the intervals into three groups, entirely left, entirely right and overlapping, and merge the overlapping ones into one

LeetCode 56 note: sort by start; if a new interval starts at or before the last merged end, merge (taking the max end), otherwise open a new one

LeetCode 54 note: keep four boundaries and walk right, down, left and up, shrinking a boundary after each side

LeetCode 49 note: use each string’s sorted form as a key; strings sharing a key form one anagram group

LeetCode 47 note: sort first, and within a level skip a value equal to the previous one when the previous one is unused

LeetCode 46 note: each level picks one unused number, marked in a used array, and records when the path is full

LeetCode 43 note: num1[i] × num2[j] lands at position i + j + 1; accumulate into an array of length n + m and carry at the end

LeetCode 40 note: each number is used once and duplicates exist, so sort, start the next level at i + 1, and skip equal values within a level

LeetCode 39 note: numbers may be reused, so the next level starts at i (not i + 1), which also avoids duplicates differing only in order