Permutations 解答

Question

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

Traditional backtracking way to solve this problem.

public class Solution {
public List<List<Integer>> permute(int[] nums) {
Arrays.sort(nums);
int length = nums.length;
List<List<Integer>> result = new ArrayList<List<Integer>>();
boolean[] visited = new boolean[length];

dfs(nums, visited, new ArrayList<Integer>(), result);
return result;
}

private void dfs(int[] nums, boolean[] visited, List<Integer> record, List<List<Integer>> result) {
if (record.size() == nums.length) {
if (!result.contains(record))
result.add(new ArrayList<Integer>(record));
return;
}
for (int i = 0; i < nums.length; i++) {
if (!visited[i]) {
record.add(nums[i]);
visited[i] = true;
dfs(nums, visited, record, result);
// Restore
record.remove(record.size() - 1);
visited[i] = false;
}
}
}
}