題目描述:Given a collection of distinct integers, return all possible permutations.
Example:
Input: [1,2,3]
Output:
[
[1,2,3],[1,3,2], [2,1,3],[2,3,1],[3,1,2],[3,2,1]
]
解題思路:與劍指offer第27題相似,求一個數組的全排列。借用一張圖來展述思路:
運用遞歸思想,依次交換當下索引數值與剩餘數組數值,然後改變當下索引下标,判斷下标值,如果達到邊界則把當下數組順序加入到集合中。依次遞歸。
代碼如下:
class Solution {
public List<List<Integer>> permute(int[] nums) {
List<List<Integer>> newList = new ArrayList<>();
permute(0, nums, newList);
return newList;
}
public void permute(int k, int[] nums, List<List<Integer>>newList) {
if (k == nums.length - 1) {
List<Integer> list = new ArrayList<>();
for (int i = 0; i < nums.length; i++)
list.add(nums[i]);
newList.add(list);
return;
}
for (int i = k; i < nums.length; i++) {
swap(nums, i, k);
permute(k + 1, nums, newList);
swap(nums, k, i);
}
}
public void swap(int[] nums, int i, int j) {
int temp = nums[i];
nums[i] = nums[j];
nums[j] = temp;
}
}