一个递归解决方案用于查找k子集排列(伪代码):
```
function kSubsetPerms(set, k):
if k == 0:
yield []
else:
for i in range(len(set)):
for perm in kSubsetPerms(set[i+1:], k-1):
yield [set[i]] + perm
```
kSubsetPermutations(partial, set, k) {
for (each element in set) {
if (k equals 1) {
store partial + element
}
else {
make copy of set
remove element from copy of set
recurse with (partial + element, copy of set, k - 1)
}
}
}
以下是一个示例:
输入:[a,b,c,d,e]
k: 3
(注:本文涉及 IT 技术)
partial = [], set = [a,b,c,d,e], k = 3
partial = [a], set = [b,c,d,e], k = 2
partial = [a,b], set = [c,d,e], k = 1 -> [a,b,c], [a,b,d], [a,b,e]
partial = [a,c], set = [b,d,e], k = 1 -> [a,c,b], [a,c,d], [a,c,e]
partial = [a,d], set = [b,c,e], k = 1 -> [a,d,b], [a,d,c], [a,d,e]
partial = [a,e], set = [b,c,d], k = 1 -> [a,e,b], [a,e,c], [a,e,d]
partial = [b], set = [a,c,d,e], k = 2
partial = [b,a], set = [c,d,e], k = 1 -> [b,a,c], [b,a,d], [b,a,e]
partial = [b,c], set = [a,d,e], k = 1 -> [b,c,a], [b,c,d], [b,c,e]
partial = [b,d], set = [a,c,e], k = 1 -> [b,d,a], [b,d,c], [b,d,e]
partial = [b,e], set = [a,c,d], k = 1 -> [b,e,a], [b,e,c], [b,e,d]
partial = [c], set = [a,b,d,e], k = 2
partial = [c,a], set = [b,d,e], k = 1 -> [c,a,b], [c,a,d], [c,a,e]
partial = [c,b], set = [a,d,e], k = 1 -> [c,b,a], [c,b,d], [c,b,e]
partial = [c,d], set = [a,b,e], k = 1 -> [c,d,a], [c,d,b], [c,d,e]
partial = [c,e], set = [a,b,d], k = 1 -> [c,e,a], [c,e,b], [c,e,d]
partial = [d], set = [a,b,c,e], k = 2
partial = [d,a], set = [b,c,e], k = 1 -> [d,a,b], [d,a,c], [d,a,e]
partial = [d,b], set = [a,c,e], k = 1 -> [d,b,a], [d,b,c], [d,b,e]
partial = [d,c], set = [a,b,e], k = 1 -> [d,c,a], [d,c,b], [d,c,e]
partial = [d,e], set = [a,b,c], k = 1 -> [d,e,a], [d,e,b], [d,e,c]
partial = [e], set = [a,b,c,d], k = 2
partial = [e,a], set = [b,c,d], k = 1 -> [e,a,b], [e,a,c], [e,a,d]
partial = [e,b], set = [a,c,d], k = 1 -> [e,b,a], [e,b,c], [e,b,d]
partial = [e,c], set = [a,b,d], k = 1 -> [e,c,a], [e,c,b], [e,c,d]
partial = [e,d], set = [a,b,c], k = 1 -> [e,d,a], [e,d,b], [e,d,c]
function kSubsetPermutations(set, k, partial) {
if (!partial) partial = [];
for (var element in set) {
if (k > 1) {
var set_copy = set.slice();
set_copy.splice(element, 1);
kSubsetPermutations(set_copy, k - 1, partial.concat([set[element]]));
}
else document.write("[" + partial.concat([set[element]]) + "] ");
}
}
kSubsetPermutations([1,2,3,4,5], 3);