LeetCode

18. 4Sum

In this problem, we use four pointers to get no repeating tuples, two for iteration and two for shrinking the solution space.

252. Meeting Rooms

We can sort the intervals by the start time, if those intervals have no overlap, then the person could attend all meetings.

56. Merge Intervals

if we sort intervals by the start endpoint of an interval, those merge-able intervals must be consecutive.