Permutations（Leet Code）

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]

.

解题代码如下：

class Solution {
public:
vector<vector<int>> result;
public:
vector<vector<int> > permute(vector<int> &num) {
int length=num.size();
perm(num,0,length-1);
return result;
}
void perm(vector<int> &num,int k,int m){
if(k==m)
result.push_back(num);
for(int i=k;i<=m;i++){
swap(num[k],num[i]);
perm(num,k+1,m);
swap(num[k],num[i]);
}
}
void swap(int &a,int &b){
int temp=a;
a=b;
b=temp;
}
};