[LeetCode] Permutations

Permutations

Given a collection of numbers, return all possible permutations.

For example,
[1,2,3] have the following permutations:
[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].

Solution: The beauty of recursion!

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public class Solution { public List<List<Integer>> permute(int[] nums) { ArrayList<List<Integer>> list = new ArrayList<List<Integer>>(); if (nums.length == 0) { return list; } if (nums.length == 1) { ArrayList<Integer> l = new ArrayList<Integer>(); l.add(nums[0]); list.add(l); return list; } List<List<Integer>> li = permute( Arrays.copyOfRange(nums, 1, nums.length) ); for (List<Integer> ll : li) { for (int i = 0; i <= ll.size(); i++) { ArrayList<Integer> l = new ArrayList<Integer>(ll); l.add(i, nums[0]); list.add(l); } } return list; } }