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| 1 | +package medium; |
| 2 | +import java.util.ArrayList; |
| 3 | +import java.util.List; |
| 4 | + |
| 5 | +public class Permutations { |
| 6 | + static class Accepted_solution { |
| 7 | + //this solution has a recursive function that has a return type |
| 8 | + public static List<List<Integer>> permute(int[] nums) { |
| 9 | + List<List<Integer>> result = new ArrayList(); |
| 10 | + result.add(new ArrayList<>()); |
| 11 | + return recursive(result, nums, 0); |
| 12 | + } |
| 13 | + |
| 14 | + private static List<List<Integer>> recursive(List<List<Integer>> result, int[] nums, |
| 15 | + int pos) { |
| 16 | + if (pos == nums.length) |
| 17 | + return result; |
| 18 | + List<List<Integer>> newResult = new ArrayList(); |
| 19 | + for (List<Integer> eachList : result) { |
| 20 | + for (int i = 0; i <= eachList.size(); i++) { |
| 21 | + List<Integer> newList = new ArrayList(eachList); |
| 22 | + newList.add(i, nums[pos]); |
| 23 | + newResult.add(newList); |
| 24 | + } |
| 25 | + } |
| 26 | + result = newResult; |
| 27 | + return recursive(result, nums, pos + 1); |
| 28 | + } |
| 29 | + } |
| 30 | + |
| 31 | + static class Accepted_solution_with_void_type { |
| 32 | + public static List<List<Integer>> permute(int[] nums) { |
| 33 | + List<List<Integer>> result = new ArrayList(); |
| 34 | + result.add(new ArrayList<>()); |
| 35 | + recursive(result, nums, 0); |
| 36 | + return result; |
| 37 | + } |
| 38 | + |
| 39 | + private static void recursive(List<List<Integer>> result, int[] nums, int pos) { |
| 40 | + if(pos == nums.length) return; |
| 41 | + List<List<Integer>> newResult = new ArrayList(); |
| 42 | + for(List<Integer> eachList : result){ |
| 43 | + for(int i = 0; i <= eachList.size(); i++){ |
| 44 | + List<Integer> newList = new ArrayList(eachList); |
| 45 | + newList.add(i, nums[pos]); |
| 46 | + newResult.add(newList); |
| 47 | + } |
| 48 | + } |
| 49 | + /**You'll have to use the two lines, instead of this line: result = newResult; otherwise, it won't work!!! Fuck!*/ |
| 50 | + result.clear(); |
| 51 | + result.addAll(newResult); |
| 52 | + |
| 53 | + //then recursion |
| 54 | + recursive(result, nums, pos+1); |
| 55 | + } |
| 56 | + } |
| 57 | + |
| 58 | + public static void main(String...args){ |
| 59 | + int[] nums = new int[]{1,2,2}; |
| 60 | + } |
| 61 | + |
| 62 | +} |
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