Medium
Two Pointers
Two Sum II - Input Array Is Sorted
Sorted input lets two pointers steer toward the target.
Approach
Start pointers at both ends. If their sum is too big, move the right pointer left; if too small, move the left pointer right. The sorted order guarantees each move discards only impossible pairs, so you find the answer in one pass with no extra memory.
Time complexity
O(n)
Space complexity
O(1)
Common mistake
Reusing the hash-map approach from Two Sum — it works but ignores the sorted structure that enables O(1) space here.
See it run, step by step
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