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42. Subsets && Subsets II

Subsets

Given a set of distinct integers, S, return all possible subsets.

Note:

  • Elements in a subset must be in non-descending order.
  • The solution set must not contain duplicate subsets.

 

For example, If S = [1,2,3], a solution is:

[  [3],  [1],  [2],  [1,2,3],  [1,3],  [2,3],  [1,2],  []]
思想: 顺序读,取前面的每个子集,把该位置数放后面作为新的子集。
class Solution {public:    vector<vector<int> > subsets(vector<int> &S) {        sort(S.begin(), S.end());        vector<vector<int> > vec(1);        for(size_t id = 0; id < S.size(); ++id) {            int n = vec.size();            while(n-- > 0) {                vec.push_back(vec[n]);                vec.back().push_back(S[id]);            }        }        return vec;    }};

 

Subsets II

Given a collection of integers that might contain duplicates, S, return all possible subsets.

Note:

  • Elements in a subset must be in non-descending order.
  • The solution set must not contain duplicate subsets.

 

For example, If S = [1,2,2], a solution is:

[  [2],  [1],  [1,2,2],  [2,2],  [1,2],  []]
思想: 排序后,按照 1 的方法。但是若前面的数字与本数字相同,则只读取含有前面数字的每个子集,把自身放在后面作为一个新的子集。
class Solution {public:    vector<vector<int> > subsetsWithDup(vector<int> &S) {        sort(S.begin(), S.end());        vector<vector<int> > vec(1);        size_t prePos, endTag;        prePos = endTag = 0;        for(size_t id = 0; id < S.size(); ++id) {            if(id > 0 && S[id] != S[id-1]) endTag = 0;            else endTag = prePos;            size_t n = vec.size();            prePos = n;            while(n > endTag) {                --n;                vec.push_back(vec[n]);                vec.back().push_back(S[id]);            }        }        return vec;    }};

 

















          

42. Subsets && Subsets II