leetCode---Subsets

一. 题目：Subsets

Given a set of distinct integers, nums, return all possible subsets.
Note: The solution set must not contain duplicate subsets.
For example,
If nums = [1,2,3], a solution is:
[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

二. 思路分析

       这题可以用backtracking的方法来解，具体思想是：在1点，然后遍历后面所有的步骤，找到所有的合理解，然后指针往后挪，不加1的情况下，从2开始，搜索以2为基础的所有合理解，然后把2移除，继续3，以此类推。所以它是一个NP搜索的过程。这题算是backtracking的经典问题。

class Solution {public:  vector<vector<int>> subsets(vector<int>& nums) {        sort(nums.begin(), nums.end());        vector<vector<int>> subs;        vector<int> sub;          genSubsets(subs, sub, nums, 0);        return subs;     }    void genSubsets(vector<vector<int>>& subs, vector<int>& sub, vector<int>& nums, int start) {        subs.push_back(sub);        for (int i = start; i < nums.size(); i++) {            sub.push_back(nums[i]);            genSubsets(subs, sub, nums, i + 1);            sub.pop_back();        }    }};