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  • 【LeetCode】040. Combination Sum II

    题目:

    Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

    Each number in C may only be used once in the combination.

    Note:

    • All numbers (including target) will be positive integers.
    • The solution set must not contain duplicate combinations.

    For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8
    A solution set is: 

    [
      [1, 7],
      [1, 2, 5],
      [2, 6],
      [1, 1, 6]
    ]
    

    题解:

    Solution 1 (TLE)

    class Solution {
    public:
        void dfs(vector<vector<int>>& vv, vector<int>& v, vector<int> candidates, int target, int sum, vector<int>& visited) {
            if(sum == target) {
                vector<int>* tmp = new vector<int>;
                *tmp = v;
                sort((*tmp).begin(), (*tmp).end());
                if(find(vv.begin(), vv.end(), *tmp) == vv.end())
                    vv.push_back(*tmp);
                delete tmp;
                return;
            }
            if(sum > target) return;
            for(int i=0; i<candidates.size(); ++i) {
                if(visited[i] != 0) continue;
                v.push_back(candidates[i]);
                visited[i] = 1;
                dfs(vv, v, candidates, target, sum+candidates[i], visited);
                v.pop_back();
                visited[i] = 0;
            }
        }
        vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
            vector<vector<int>> vv;
            vector<int> v;
            vector<int> visited(candidates.size(),0);
            dfs(vv, v, candidates, target, 0, visited);
            return vv;        
        }
    };

      Solution 1 中即使i从level开始遍历,也无法accepted,加入stop后才勉强通过,即Solution 2 

    Solution 2 (almost TLE but not 579ms)

    class Solution {
    public:
        void dfs(vector<vector<int>>& vv, vector<int>& v, vector<int> candidates, int target, int sum, vector<int>& visited, int stop,int level) {
            if(sum == target) {
                vector<int>* tmp = new vector<int>;
                *tmp = v;
                sort((*tmp).begin(), (*tmp).end());
                if(find(vv.begin(), vv.end(), *tmp) == vv.end())
                    vv.push_back(*tmp);
                delete tmp;
                return;
            }
            if(sum > target) {stop = 1;return;}
            for(int i=level; i<candidates.size(); ++i) {
                if(visited[i] != 0) continue;
                v.push_back(candidates[i]);
                visited[i] = 1;
                dfs(vv, v, candidates, target, sum+candidates[i], visited, stop, level+1);
                if(stop == 1) {stop = 0;break;}
                v.pop_back();
                visited[i] = 0;
            }
        }
        vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
            vector<vector<int>> vv;
            vector<int> v;
            vector<int> visited(candidates.size(),0);
            sort(candidates.begin(), candidates.end());
            dfs(vv, v, candidates, target, 0, visited, 0, 0);
            return vv;        
        }
    };

    Solution 3 ()

    class Solution {
    public:
        void dfs(vector<vector<int>>& vv, vector<int>& v, vector<int> candidates, int target, vector<int>& visited, int stop,int level) {
            if(target == 0) {
                vector<int>* tmp = new vector<int>;
                *tmp = v;
                sort((*tmp).begin(), (*tmp).end());
                if(find(vv.begin(), vv.end(), *tmp) == vv.end())
                    vv.push_back(*tmp);
                delete tmp;
                return;
            }
            if(target<0) {stop = 1;return;}
            for(int i=level; i<candidates.size(); ++i) {
                if(visited[i] != 0) continue;
                v.push_back(candidates[i]);
                visited[i] = 1;
                dfs(vv, v, candidates, target-candidates[i], visited, stop,level+1);
                if(stop == 1) {stop = 0;break;}
                v.pop_back();
                visited[i] = 0;
            }
        }
        vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
            vector<vector<int>> vv;
            vector<int> v;
            vector<int> visited(candidates.size(),0);
            sort(candidates.begin(), candidates.end());
            dfs(vv, v, candidates, target, visited, 0,0);
            return vv;        
        }
    };

    Solution 4 

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  • 原文地址:https://www.cnblogs.com/Atanisi/p/6789004.html
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