Javascript 堆的算法（非递归）

Question

I have implemented Heap's non-recursive algorithm in JavaScript. When checking permutations with console.log(arr) everything works as expected. But when I try to push each permutation to a result array, then everything breaks up. It just returns result filled with last iteration permutation.

 function generate(n, arr) { function swap(item1, item2){ console.log(item1, item2); let tmp = arr[item1]; arr[item1] = arr[item2]; arr[item2] = tmp; } var c = []; var allPermutations = []; for (let i = 0; i < n; i++) { c[i] = 0; } console.log(arr); allPermutations.push(arr); for (let i = 1; i < n; i) { if (c[i] < i) { if (i % 2 == 0) { swap(0, i); } else { swap(c[i], i); } console.log(arr); allPermutations.push(arr); c[i] += 1; i = 1; } else { c[i] = 0; i += 1; } } return allPermutations; } console.log('result', generate(3, ["a", "a", "b"]));

Answer 1

The problem is that arrays are just references so when you push in the array you are just pushing a reference to it. So, on the next iteration you update the array and when you look at the final output, all the indexes will be the same since it is the same array.

So what can you do? clone it.

allPermutations.push(arr.slice(0));

Answer 2

Yep - its a reference problem. Alternative to epascarello's answer:

allPermutations.push([...arr]);