Longest All-Distinct Window

**Description:** Print the length of the longest contiguous window with all distinct values. **Input:** Line 1: n (1 <= n <= 200000). Line 2: n integers (0 <= a[i] <= 10^6). **Output:** One integer — the longest all-distinct run. **Example:** 6 / 1 2 3 1 2 3 -> 3.