LeetCode 46.Permutations
                                            
                                            제목:
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] .
분석과 해답: 간단하게 dfs로 귀속시키면 됩니다...
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