LeetJava/KSum.java at master · ysdeal/LeetJava · GitHub

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/*
K Sum
*/

import java.util.*;
public class KSum{
	public static void main(String[] args) {
		int[] num = {-5,-4,-3,-2, 1, 3,3,5};
		System.out.println(fourSum(num,-11));
		//System.out.println(findSumFromSortArray(num,0,2,-2));
	}

	public static List<List<Integer>> findSumFromSortArray(int[] num, int bg, int count, int target){
		List<List<Integer>> res = new ArrayList<List<Integer>>();
		HashSet<Integer> visited = new HashSet<Integer>();
		if(count == 2){
           int i = bg, j = num.length - 1;

           while(i < j){
           	int sum = num[i] + num[j];
           	if(sum == target && !visited.contains(num[i])
           	   && !visited.contains(num[j])){
           	   	List<Integer> tp = new ArrayList<Integer>(Arrays.asList(num[i],num[j]));
                 res.add(tp);
                 visited.add(num[i]);
                 visited.add(num[j]);
                 i++;
                 j--;

           	}else if (sum < target)
           	   i++;
           	else
           	   j--;
           }

		}else{

              for(int i = bg; i < num.length; ++i){

              	if(visited.contains(num[i]))
              		continue;
              	visited.add(num[i]);
              	List<List<Integer>> subRes = findSumFromSortArray(num, i + 1, count - 1, target - num[i]);
              	if(subRes != null){
              		for(List<Integer> sb : subRes)
              			sb.add(0,num[i]);

              		res.addAll(subRes);

              	}
              }
		}

		return res;
	}

	public static List<List<Integer>> fourSum(int[] num,int target){
		Arrays.sort(num);
		return findSumFromSortArray(num,0, 4, target);
	}
}