leetcode39:Combination Sum

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/Somnus_k/article/details/82802396

思路：将数组中的每个点作为根节点，然后采用深度优先遍历即可，由于数字可以重复使用，所以递归时候注意下标。

代码：

public class CombinationSum39 {

	public static void main(String[] args) {
		int[] num ={2,3,5};
		
		System.out.println(combinationSum(num,8));
	}

	public static List<List<Integer>> combinationSum(int[] candidates, int target) {
		List<List<Integer>> ls =new ArrayList<>();
		List<Integer> list = new ArrayList<>();
		helpCombinationSum(candidates,target,0,ls,list);
		return ls;
	}

	private static void helpCombinationSum(int[] num, int target, int index, List<List<Integer>> ls,
			List<Integer> list) {
		if(index>=num.length||target<0)
			return;
		if(target==0)
			ls.add(new ArrayList(list));
		for (int i = index; i < num.length; i++) {
			list.add(num[i]);
			helpCombinationSum(num, target-num[i], i, ls, list);
			list.remove(list.size()-1);
		}
		
	}
}

输出：