题目链接

回溯

class Solution {List<List<Integer>> res = new ArrayList<List<Integer>>();List<Integer> list = new ArrayList<Integer>();public List<List<Integer>> combinationSum(int[] candidates, int target) {backtracking(candidates, target, 0, 0);return res;}public void backtracking(int[] candidates, int target, int sum, int startIndex){if(sum > target){return;}if(sum == target){res.add(new ArrayList<>(list));return;}for(int i = startIndex; i < candidates.length; i++){sum += candidates[i];list.add(candidates[i]);// 数字可以无限制重复被选取，所以i不用+1backtracking(candidates, target, sum, i);sum -= candidates[i];list.removeLast();}}
}