Permutations by swapping: Difference between revisions

if //r.put((i % 2 ? iota(cast(int)item.length, -1, -1) :

// r ~= iota(cast(int)item.length, -1,+ -1))

// .map!(i => item[0 .. i] ~ (items-1) ~ item[i..$]));

immutable f=(in int i)=>item[0..i] ~ (items-1) ~ item[i..array$];

elser ~= (i % 2) ?

r ~= iota(cast(int)item.length, +-1, -1).map!f.array :

.map!iota(i => item[0 ..length i]+ ~ (items-1) ~ item[i.map!f.$])array;

//return sPermu(n).zip([1, -1].cycle);