LeetCode: Permutations [045]

【题目】

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].

【题意】

给定一个数组，生成所有的全排列

【思路】

递归，类DFS

【代码】

class Solution {
public:
    void dfs(vector<vector<int> >&result, vector<int>combination, vector<int>candidates, int index2remove){
        //combination——当前已生成的组合
        //candidates——候选数字集合
        //index2remove——添加到combination的下一个数字在candidates中的索引位
        combination.push_back(candidates[index2remove]);
        candidates.erase(candidates.begin()+index2remove);
        if(candidates.empty()){
            result.push_back(combination);
        }
        else{
            for(int i=0; i<candidates.size(); i++){
                dfs(result, combination, candidates, i);
            }
        }

    }
    vector<vector<int> > permute(vector<int> &num) {
        vector<vector<int> >result;
        int size=num.size();
        if(size==0)return result;

        vector<int> combination;
        for(int i=0; i<num.size(); i++){
            dfs(result, combination, num, i);
        }
        return result;
    }
};

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