You are given two nondecreasing arrays A (length n) and B (length m) of non-negative integers and an integer k (1 <= k <= n*m). Return the k-th smallest value among all pair sums A[i] + B[j]. You must avoid materializing all n*m pairs. Target complexity: O(k log min(n, m)) time and O(min(n, m)) extra space using a min-heap. Approach: iterate over the shorter array so the heap holds at most min(n, m) entries. Seed the heap with the pair (smaller[i] + larger[0], i, 0) for every index i of the shorter array. Because both arrays are sorted, the smallest unseen sum is always the heap top. Pop k times; each time you pop (sum, i, j), push the next candidate in the same row (smaller[i] + larger[j+1]) if it exists. The k-th popped value is the answer. Duplicate sums are returned with multiplicity — the k-th smallest counts repeated sums separately, exactly as a fully sorted list of all pair sums would. Return an integer (the k-th smallest pair sum).