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Find the Duplicate Number Without Modifying the Array

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Problem statement

An array of length n+1 contains values from 1 through n. Exactly one value occurs more than once.

Return that duplicate without modifying the array and using constant extra space.

Function

findDuplicate(nums: int[]) → int

Examples

Example 1

nums = [1,3,4,2,2]return = 2

Two is the repeated value.

Example 2

nums = [3,1,3,4,2]return = 3

Three is repeated.

Example 3

nums = [1,1]return = 1

The smallest valid array repeats one.

Constraints

1 <= n <= 100000.
Exactly one distinct value is duplicated, possibly more than twice.