leetcode--Combination Sum

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, … , a_k) must be in non-descending order. (ie, a₁ ≤ a₂ ≤ … ≤ a_k).
• 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]

[java]  view plain  copy

1. public class Solution {  
2.     public List<List<Integer>> combinationSum(int[] candidates, int target) {  
3.         List<List<Integer>> res = new ArrayList<List<Integer>>();  
4.         Arrays.sort(candidates);  
5.         Stack<Integer> stack = new Stack<Integer>();  
6.         dfs(res, stack, target, 0, candidates,0);  
7.         return res;  
8.     }  
9.       
10.     void dfs(List<List<Integer>> res,Stack<Integer> stack,int target,int cur,int[] arr,int sum){        
11.         if(sum==target){  
12.             ArrayList<Integer> data = new ArrayList<Integer>(stack);  
13.             res.add(data);  
14.             return;  
15.         }else if(sum>target) return;  
16.         else{  
17.             for(int i=cur;i<arr.length;i++){  
18.                 stack.add(arr[i]);  
19.                 sum += arr[i];  
20.                 dfs(res, stack, target, i, arr,sum);  
21.                 sum -= arr[i];  
22.                 stack.pop();  
23.             }  
24.         }  
25.     }  
26. }  

原文链接http://blog.youkuaiyun.com/crazy__chen/article/details/45725483