nth permutation

• https://stackoverflow.com/questions/33984004/finding-nth-permutation-for-parallelized-c-c
• Write a program to print all permutations of a given string
• how to find nth permutation of a string in c
• https://en.wikipedia.org/wiki/Factorial_number_system
• https://math.stackexchange.com/questions/60742/finding-the-n-th-lexicographic-permutation-of-a-string
• https://stackoverflow.com/questions/8059150/efficient-calculation-of-nth-item-in-a-random-permutation
• Permutations with CUDA and OpenCL

next permutation

• https://stackoverflow.com/questions/4972470/what-is-the-time-complexity-of-stdnext-permutation-function-in-c
• https://stackoverflow.com/questions/4973077/the-amortized-complexity-of-stdnext-permutation
• http://www.sgi.com/tech/stl/next_permutation.html