I need to get all possible subsets of an array.
Say I have this:
[1, 2, 3]
How do I get this?
[], [1], [2], [1, 2], [2, 3], [1, 3], [1, 2, 3]
I am interested in all subsets. For subsets of specific length, refer to the following questions:
Here is one more very elegant solution with no loops or recursion, only using the map and reduce array native functions.
const getAllSubsets =
theArray => theArray.reduce(
(subsets, value) => subsets.concat(
subsets.map(set => [value,...set])
),
[[]]
);
console.log(getAllSubsets([1,2,3]));
We can solve this problem for a subset of the input array, starting from offset
. Then we recurse back to get a complete solution.
Using a generator function allows us to iterate through subsets with constant memory usage:
// Generate all array subsets:
function* subsets(array, offset = 0) {
while (offset < array.length) {
let first = array[offset++];
for (let subset of subsets(array, offset)) {
subset.push(first);
yield subset;
}
}
yield [];
}
// Example:
for (let subset of subsets([1, 2, 3])) {
console.log(subset);
}
Runtime complexity is proportional to the number of solutions (2ⁿ) times the average length per solution (n/2) = O(n2ⁿ).
Another simple solution.
function getCombinations(array) {
function fork(i, t) {
if (i === array.length) {
result.push(t);
return;
}
fork(i + 1, t.concat([array[i]]));
fork(i + 1, t);
}
var result = [];
fork(0, []);
return result;
}
var data = [1, 2, 3],
result = getCombinations(data);
console.log(result);
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You can easily generate the powerset from an array, using something like the following:
var arr = [1, 2, 3];
function generatePowerSet(array) {
var result = [];
result.push([]);
for (var i = 1; i < (1 << array.length); i++) {
var subset = [];
for (var j = 0; j < array.length; j++)
if (i & (1 << j))
subset.push(array[j]);
result.push(subset);
}
return result;
}
console.log(generatePowerSet(arr));
Throughout the main loop of the function, subsets are created and then pushed into the result
array.
let subsets = (n) => {
let result = [];
result.push([]);
n.forEach(a => {
//array length
let length = result.length;
let i =0;
while(i < length){
let temp = result[i].slice(0);
temp.push(a);
result.push(temp);
i++;
}
})
return result;
}
This one is with recursion
var subsets = function(s){
if(s.length === 0) {
return [[]]
}
var h,t,ss_excl_h;
var ss_incl_h = [];
[h,...t] = s;
ss_excl_h = subsets(t)
for(ss of ss_excl_h) {
let hArr = [];
hArr.push(h);
let temp = hArr.concat(ss)
ss_incl_h.push(temp);
}
return ss_incl_h.concat(ss_excl_h)
}
console.log(subsets([1,2,3])) // returns distinct subsets
来源:https://stackoverflow.com/questions/42773836/how-to-find-all-subsets-of-a-set-in-javascript