全排列2 · Permutations
Posted immiao0319
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Given a collection of numbers that might contain duplicates, return all possible unique permutations.
Example:
Input: [1,1,2]
Output:
[
[1,1,2],
[1,2,1],
[2,1,1]
]
数组记得要排序
一些问题不能理解,那就这样吧。本来中等的题目就不好理解,得考虑一下投入产出比了。
public class Solution { /* * @param nums: A list of integers. * @return: A list of permutations. */ public List<List<Integer>> permuteUnique(int[] nums) { //corner case List<List<Integer>> results = new ArrayList<>(); List<Integer> permutations = new ArrayList<>(); int[] visited = new int[nums.length]; if (nums == null) { return null; } if (nums.length == 0) { //return new ArrayList<>(); results.add(new ArrayList<>()); return results; } Arrays.sort(nums); for (int i = 0; i < nums.length; i++) { visited[i] = 0; } //helper helper(nums, permutations, visited, results); //return return results; } //helper public void helper (int[] nums, List<Integer> permutations, int[] visited, List<List<Integer>> results) { if (permutations.size() == nums.length) { results.add(new ArrayList<>(permutations)); return ;// } for (int i = 0; i < nums.length; i++) { if (visited[i] == 1) continue; if ((i != 0) && (nums[i] == nums[i - 1]) && (visited[i - 1] == 0)) continue; permutations.add(nums[i]); visited[i] = 1; helper(nums, permutations, visited, results); visited[i] = 0; permutations.remove(permutations.size() - 1); } } }
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