Leetcode 1956. Minimum Time For K Virus Variants to Spread

Given a grid/graph with candidate infected cells and K virus variants that spread over time according to local adjacency rules (and possibly obstacles), find the minimum time required for K chosen sources/variants to infect the entire region. This requires deciding whether a proposed time is feasible (typically using multi-source reachability/coverage checks) and optimizing that time—often solved with binary search over time combined with BFS/graph-connectivity or flow-based feasibility tests.