[LeetCode] 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].

Solution:

对一个没有重复元素的序列做全排序，可以考虑采用递归的思路。n个元素的全排列为n个元素分别作为第一个元素，并加上分别去除首元素剩下元素的全排列。当序列递归到只有一个元素时，

递归终止，一个可行的全排列产生。

class Solution {
public:vector<vector<int> > ans;vector<int> src;int len;void perm(int i){if(i == len - 1){//a new permutation comesvector<int> tmp;for(int i = 0;i < len;i++)tmp.push_back(src[i]);ans.push_back(tmp);return;}else{for(int k = i;k < len;k++){int tmp = src[i];src[i] = src[k];src[k] = tmp;perm(i + 1);src[k] = src[i];src[i] = tmp;}}}vector<vector<int> > permute(vector<int> &num) {len = num.size();if(len == 0) return ans;src = num;perm(0);return ans;}
};

转载于:https://www.cnblogs.com/changchengxiao/p/3608941.html

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