[LeetCode]40.Combination Sum II
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【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.
- Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
- 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]
【分析】
基本思路是先排好序,然后每次递归中把剩下的元素一一加到结果集合中,并且把目标减去加入的元素,然后把剩下元素(包括当前加入的元素)放到下一层递归中解决子问题。以start记录我们选到了第几个值,并且一直往后选,这样可以避免选到重复的子集。
这一题和上一题:点击打开链接差不多一样的思路,只要稍作修改就行。只要在for循环中加一个判断条件即可:
if(i > start && candidates[i] == candidates[i-1]){continue;}
这个判断的目的是排除同一层次相同元素的出现。例如:下面例题中有两个1,在第一次递归中不能都出现1,可以的是第一次递归出现1,第二次递归也可以出现一个1
/********************************** 日期:2015-01-27* 作者:SJF0115* 题目: 40.Combination Sum II* 网址:https://oj.leetcode.com/problems/combination-sum-ii/* 结果:AC* 来源:LeetCode* 博客:**********************************/#include <iostream>#include <vector>#include <algorithm>using namespace std;class Solution {public: vector<vector<int> > combinationSum2(vector<int> &candidates, int target) { // 中间结果 vector<int> path; // 最终结果 vector<vector<int> > result; int size = candidates.size(); if(size <= 0){ return result; }//if // 排序 sort(candidates.begin(),candidates.end()); // 递归 DFS(candidates,target,0,path,result); return result; }private: void DFS(vector<int> &candidates, int target,int start,vector<int> &path,vector<vector<int> > &result){ int len = candidates.size(); // 找到一组组合和为target if(target == 0){ result.push_back(path); return; }//if for(int i = start;i < len;++i){ // 同一层次不能出现相同元素 if(i > start && candidates[i] == candidates[i-1]){ continue; }//if // 剪枝 if(target < candidates[i]){ return; }//if path.push_back(candidates[i]); DFS(candidates,target-candidates[i],i+1,path,result); path.pop_back(); }//for }};int main(){ Solution solution; int target = 8; vector<int> vec; vec.push_back(10); vec.push_back(1); vec.push_back(2); vec.push_back(7); vec.push_back(6); vec.push_back(1); vec.push_back(5); vector<vector<int> > result = solution.combinationSum2(vec,target); // 输出 for(int i = 0;i < result.size();++i){ for(int j = 0;j < result[i].size();++j){ cout<<result[i][j]<<" "; } cout<<endl; } return 0;}
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