Medium
Intervals
Merge Intervals
Sort by start, then merge any interval that overlaps the last one kept.
Approach
Sort intervals by start time. Walk through them, and if the current interval starts before the previous merged one ends, extend that merged interval's end; otherwise push a new interval. One sort plus one sweep.
Time complexity
O(n log n)
Space complexity
O(n)
Common mistake
Forgetting to sort first — merging only works once intervals are ordered by start.
See it run, step by step
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