【Permutations】cpp

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].

代码:

class Solution {
public:
    vector<vector<int>> permute(vector<int>& nums) {
            vector<vector<int> > ret;
            vector<int> none;
            ret.push_back(none);
            for ( size_t i = 0; i < nums.size(); ++i ){
                vector<vector<int> > tmp = ret;
                ret.clear();
                for ( size_t j = 0; j < tmp.size(); ++j ){
                    for ( size_t k = 0; k < i+1; ++k ){
                        vector<int> ori = tmp[j];
                        ori.insert(ori.begin()+k, nums[i]);
                        ret.push_back(ori);
                    }
                }
            }
            return ret;
    }
};

tips:

参考(http://bangbingsyb.blogspot.sg/2014/11/leetcode-permutations-i-ii.html

采用增量构造法(暴力法解决):每次新增一个元素,对上次已有的permutations,从0到size挨个位置插入一遍。

[]  // 注意一开始要给ret一个空的vector<int> 这样才循环才能run起来

[1]

[2 1],[1 2]

[3 2 1], [2 3 1], [2 1 3], [3 1 2 ], [1 3 2], [1 2 3]

时间: 2024-11-09 16:13:16

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