0000 - 0099
0046 - Permutations (Medium)
Problem Link
https://leetcode.com/problems/permutations/
Problem Statement
Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.
Example 1:
Input: nums = [1,2,3]
Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]Example 2:
Input: nums = [0,1]
Output: [[0,1],[1,0]]Example 3:
Input: nums = [1]
Output: [[1]]Constraints:
1 <= nums.length <= 6-10 <= nums[i] <= 10- All the integers of
numsare unique.
Approach 1: STL
Use C++ STL next_permutation to generate all possible permutations.
class Solution {
public:
vector<vector<int>> permute(vector<int>& nums) {
vector<vector<int>> ans;
sort(nums.begin(), nums.end());
do {
ans.push_back(nums);
} while(next_permutation(nums.begin(), nums.end()));
return ans;
}
};Approach 2: Backtracking
Check out Backtracking section for the detailed explanation.
class Solution {
public:
void backtrack(vector<int>& nums, vector<vector<int>>& ans, vector<int>& tmp) {
if ((int) tmp.size() == (int) nums.size()) {
ans.push_back(tmp);
return;
}
for (auto x : nums) {
if (find(tmp.begin(), tmp.end(), x) != tmp.end()) continue;
tmp.push_back(x);
backtrack(nums, ans, tmp);
tmp.pop_back();
}
}
vector<vector<int>> permute(vector<int>& nums) {
// sort(nums.begin(), nums.end());
vector<vector<int>> ans;
vector<int> tmp;
backtrack(nums, ans, tmp);
return ans;
}
};class Solution:
def permute(self, nums: List[int]) -> List[List[int]]:
res = []
if (len(nums) == 1):
return [nums.copy()]
for i in range(len(nums)):
n = nums.pop(0)
perms = self.permute(nums)
for perm in perms:
perm.append(n)
res.extend(perms)
nums.append(n)
return res