  The problem of packing unequal circles into a circular container stands as a
classic and challenging optimization problem in computational geometry. This
study introduces a suite of innovative and efficient methods to tackle this
problem. Firstly, we present a novel layout-graph transformation method that
represents configurations as graphs, together with an inexact hash method
facilitating fast comparison of configurations for isomorphism or similarity.
Leveraging these advancements, we propose an Iterative Solution-Hashing Search
algorithm adept at circumventing redundant exploration through efficient
configuration recording. Additionally, we introduce several enhancements to
refine the optimization and search processes, including an adaptive adjacency
maintenance method, an efficient vacancy detection technique, and a
Voronoi-based locating method. Through comprehensive computational experiments
across various benchmark instances, our algorithm demonstrates superior
performance over existing state-of-the-art methods, showcasing remarkable
applicability and versatility. Notably, our algorithm surpasses the best-known
results for 56 out of 179 benchmark instances while achieving parity with the
remaining instances.
