6. Longest Consecutive Sequence
Find the longest sequence of integer values that increase by exactly one. The values may be scattered throughout the input; you are measuring a run of values, not a continuous slice of the array.
Repeated occurrences of the same value do not extend a run. For example, the values 1, 2, 3, and 4 form a length-four run regardless of their input order.
Example 1
Input
[100,4,200,1,3,2]
Output
4
Explanation: The values 1,2,3,4 form a run of length four even though they are scattered through the array.
Example 2
Input
[1,2,2,3]
Output
3
Explanation: The repeated 2 does not lengthen or break the run 1,2,3.
Example 3
Input
[-2147483648,2147483647]
Output
1
Explanation: The two extreme int values must not wrap around and appear consecutive.
Constraints
0 <= nums.length <= 105-231 <= nums[i] <= 231 - 1
Hints
Hint 1
Which operation do you repeat when extending a consecutive run? Store membership rather than input positions.
Hint 2
Every run has a unique smallest value. How can you recognize it without sorting?
Hint 3
Only launch scans from values whose predecessor is absent. Iterate distinct values and guard integer boundaries.
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Scattered run
[100,4,200,1,3,2]
4