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Find the smallest positive integer missing from an unsorted array while meeting O(n) time and O(1) extra space. The classic approach uses in-place index-based placement (place value v at index v-1) and then scans for the first index where arr[i] != i+1 to identify the missing positive integer.
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Lyft
Leetcode 41. First Missing Positive
Reported May 17, 2026 · 1 source report
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Source snapshot: Nov 12, 2026
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