Given two integer arrays nums1 and nums2 of equal length, find the minimum index sum $i + j$ such that nums1[i] == nums2[j].

Return the minimum index sum among all common elements. If there are no common elements between nums1 and nums2, return $-1$.

Constraints:

• $1 \leq$ nums1.length $=$ nums2.length $\leq 10^5$

• $-10^5 \leq$ nums1[i], nums2[i] $\leq 10^5$

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