[leedcode 46] Permutations

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]

.

public class Solution {
//全排列：构造一个递归函数，函数的参数一个代表开始排列的索引，一个代表最终排列的索引
//每一位与开始位进行交换，再递归start+1到end，注意结果的保存
List<Integer> seq;
List<List<Integer>> res;
public List<List<Integer>> permute(int[] nums) {
seq=new ArrayList<Integer>();
res=new ArrayList<List<Integer>>();
findpermute(nums,0,nums.length-1);
return res;

}
public void findpermute(int []nums,int start,int end){
if(start>end){
res.add(new ArrayList<Integer>(seq));//注意要重新new一个
return ;
}

for(int i=start;i<=end;i++){
swap(nums,start,i);
seq.add(nums[start]);
findpermute(nums,start+1,end);
seq.remove(seq.size()-1);//注意删除
swap(nums,start,i);
}
}
public void swap(int[] nums,int i,int j){
int temp=nums[i];
nums[i]=nums[j];
nums[j]=temp;
}
}