public static void swap(Map<Long, Long> permutation, long i, long j) {
		if (i == j) {
			return;
		}
		long ith = permutation.getOrDefault(i, i);
		long jth = permutation.getOrDefault(j, j);
		permutation.put(i, jth);
		permutation.put(j, ith);
	}
Updates a Map<Long,Long> treated as a permutation p to produce a new permutation p'
such that p'(i) = p(j) and p'(j) = p(i).  For i not in the keySet of the map, it is
assumed that p(i) = i.
@param permutation permutation map
@param i index
@param j index
Ghidra/Extensions/MachineLearning/src/main/java/ghidra/machinelearning/functionfinding/RandomSubsetUtils.java