On the Harmonious Coloring of Graphs
John E. Hopcroft, Mukkai S. Krishnamoorthy · SIAM Journal on Algebraic and Discrete Methods · 1983
In this report we define a new coloring of graphs, namely harmonious coloring of graphs, which arises as an extension of harmonious and graceful numbering of graphs. We show that the harmonious coloring problem for general graphs is NP-complete.