46. Permutations

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]

,
and

[3,2,1]

.
【思路】求给定向量数组所有元素的全排列问题。

n个元素有n!种全排列，而STL底层文件<
algorithm >中有关于排列元素的标准算法：

bool next_permutation(BidirectionalIterator beg , BidirectionalIterator end);

该函数会改变区间[beg , end)内的元素次序，使它们符合“下一个排列次序”

bool prev_permutation(BidirectionalIterator beg , BidirectionalIterator end);

该函数会改变区间[beg , end)内的元素次序，使它们符合“上一个排列次序”

class Solution {
public:
vector<vector<int>> permute(vector<int>& nums) {
vector<vector<int>> re;
if(nums.size()==0) return re;
sort(nums.begin(), nums.end());
re.push_back(nums);
while(next_permutation(nums.begin(),nums.end()))
{
re.push_back(nums);
}
return re;
}
};