Two PointersTwo Pointers

Two Pointers (Same Direction)

A read pointer scans every element while a write pointer marks the end of the finished prefix, compacting or filtering an array in place in one pass.

Learn Two Pointers (Same Direction) →
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0
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1
↑write↑read
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1/20Remove duplicates in place. a[0] is always unique, so write starts at 1: everything before write is the deduplicated prefix.
write pointerread pointerUnique prefixDuplicate (skipped)
PseudocodeLearn Two Pointers (Same Direction) →
1write = 1
2for read in 1 .. n-1:
3  if a[read] != a[write-1]:
4    a[write] = a[read]
5    write += 1
6return write  # length of unique prefix
Variables
write1
read1
Complexity
best O(n)
avg O(n)
worst O(n)
space O(1)
Speed