LeetCode 39 Combination Sum(满足求和等于target的所有组合)

package leetcode_50;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;


/***
 * 
 * @author pengfei_zheng
 * 求解满足加和等于target的所有数字组合
 */
public class Solution39 {
    public List<List<Integer>> combinationSum(int[] nums, int target) {
        List<List<Integer>> list = new ArrayList<>();
        Arrays.sort(nums);
        backtrack(list, new ArrayList<>(), nums, target, 0);
        return list;
    }

    private void backtrack(List<List<Integer>> list, List<Integer> tempList, int [] nums, int remain, int start){
        if(remain < 0) return;
        else if(remain == 0) list.add(new ArrayList<>(tempList));
        else{ 
            for(int i = start; i < nums.length; i++){
                tempList.add(nums[i]);
                backtrack(list, tempList, nums, remain - nums[i], i); // not i + 1 because we can reuse same elements
                tempList.remove(tempList.size() - 1);
            }
        }
    }
}