Given a collection of distinct 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],
[3,2,1]
]
题意：求一个字符串的全排序。
用递归，dfs来实现。
java代码：
private List<Integer> temp = new ArrayList<>();
public List<List<Integer>> permute(int[] nums) {
List<List<Integer>> list = new ArrayList<>();
dfs(list, nums, 0);
return list;
}
private void swap(int[] nums, int i, int j) {
int temp = nums[i];
nums[i] = nums[j];
nums[j] = temp;
}
private void dfs(List<List<Integer>> list, int[] nums, int j) {
if (j == nums.length) {
for (int num : nums)
temp.add(num);
list.add(temp);
temp = new ArrayList<>();
}
for (int i = j; i < nums.length; i++) {
swap(nums, i, j);
dfs(list, nums, j+1);
swap(nums, i, j);
}
}
