Two Pointers
EasyOn a sorted array, one pointer at each end. Move the pointer that can only push the sum in the direction you need.
sorted arraylinear
TimeO(n)
SpaceO(1)
Inputsorted numbers | target sum
2
0
3
1
5
2
8
3
11
4
15
5
target16
Find two values summing to 16.
steps0
1 / 9
l = 0; r = n - 1
while l < r:
sum = a[l] + a[r]
if sum == target: return [l, r]
if sum < target: l++
else: r--
Why it matters
Each pointer only moves inward, so together they take at most n steps.
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