39. Combination Sum - jiejackyzhang/leetcode-note GitHub Wiki
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.
- 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] ]
解题思路为backtracking。
public class Solution {
public List<List<Integer>> combinationSum(int[] candidates, int target) {
List<List<Integer>> res = new ArrayList<List<Integer>>();
Arrays.sort(candidates);
helper(candidates, target, 0, new ArrayList<Integer>(), res);
return res;
}
private void helper(int[] candidates, int target, int index, List<Integer> sofar, List<List<Integer>> res) {
if(target < 0) return;
if(index >= candidates.length) return;
if(target == 0) {
res.add(new ArrayList<Integer>(sofar));
return;
}
// with current candidate
sofar.add(candidates[index]);
helper(candidates, target-candidates[index], index, sofar, res);
sofar.remove(sofar.size()-1);
// without current candidate
helper(candidates, target, index+1, sofar, res);
}
}