LeetCode-46. Permutations

Given a collection of distinct numbers, return all possible permutations.

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

1
2
3
4
5
6
7
8
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]

思路

对于nums数组中的每一个数,都依次放入结果集中,如果结果集中已经包含这个数,就继续下一次循环。

以数组[1,2,3]为例,每次循环的结果是:

1
2
3
4
5
6
[1,2,3]
[1,3,2]
[2,1,3]
[2,3,1]
[3,1,2]
[3,2,1]

代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
public List<List<Integer>> permute(int[] nums) {
List<List<Integer>> list = new ArrayList<>();
backtrack(list, new ArrayList<>(), nums);
return list;
}

private void backtrack(List<List<Integer>> list, List<Integer> tempList, int [] nums){
if(tempList.size() == nums.length){
list.add(new ArrayList<>(tempList));
} else{
for(int i = 0; i < nums.length; i++){
if(tempList.contains(nums[i])) continue;
tempList.add(nums[i]);
backtrack(list, tempList, nums);
tempList.remove(tempList.size() - 1);
}
}
}

-------------本文结束感谢您的阅读-------------
Thank you for your encouragement