Leetcode | Combination Sum I && II
2014-05-18 11:28
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Combination Sum I
Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.The same repeated number may be chosen from C unlimited number of times.
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 2,3,6,7 and target 7,
A solution set is:
[7]
[2, 2, 3]
先排序,然后每次从当前位置开始找下一个数。去下重,不过貌似leetcode的testcases没有针对这个。
class Solution { public: vector<vector<int> > combinationSum(vector<int> &candidates, int target) { vector<vector<int> > ans; if (candidates.empty()) return ans; vector<int> tmp; sort(candidates.begin(), candidates.end()); recurse(candidates, 0, target, tmp, ans); return ans; } void recurse(vector<int> &candidates, int start, int target, vector<int> &tmp, vector<vector<int> > &ans) { if (target < 0) return; if (target == 0) { ans.push_back(tmp); return; } for (int i = start; i < candidates.size(); i++) { tmp.push_back(candidates[i]); recurse(candidates, i, target - candidates[i], tmp, ans); tmp.pop_back(); } } };
Combination Sum II
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]
这道题和上面类似。但是每个数只能使用一次。如果是重复数,在每个位置上用的应该是第一个数,这样才能保证这个重复数可以重复使用。
比如[1,1,2,3],如果每个位置用的是重复数的最后一个,那么就生成不了[1,1,2]了。
class Solution { public: vector<vector<int> > combinationSum2(vector<int> &num, int target) { sort(num.begin(), num.end()); vector<int> r; recursive(num, target, 0, r); return ret; } void recursive(vector<int> &num, int target, int start, vector<int> &r) { if (target <= 0) { if (0 == target) ret.push_back(r); return; } for (int i = start; i < num.size(); ++i) { if (i > start && num[i] == num[i - 1]) continue; r.push_back(num[i]); recursive(num, target - num[i], i + 1, r); r.pop_back(); } } private: vector<vector<int> > ret; };
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