【Leetcode- 18】4Sum

【Leetcode- 18】4Sum

/*Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note:

The solution set must not contain duplicate quadruplets.

Example:

Given array nums = [1, 0, -1, 0, -2, 2], and target = 0.

A solution set is:
[
[-1, 0, 0, 1],
[-2, -1, 1, 2],
[-2, 0, 0, 2]
]
*/

方法，按照3Sum问题解答，这种方法不是特别快

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

public class Solution18 {
	
    public List<List<Integer>> fourSum(int[] nums, int target) {
    	List<List<Integer>>  list=new ArrayList<List<Integer>>();
    	int len=nums.length;
    	Arrays.sort(nums);
    	for(int i=0;i<len;i++) {
    		for(int j=i+1;j<len;j++) {
    			int L=j+1;
    			int R=len-1;
    			while(L<R) {
    				int value=nums[i]+nums[j]+nums[L]+nums[R];
    				if(value==target) {
    					List<Integer> l=new ArrayList<Integer>();
    					l.add(nums[i]);
    					l.add(nums[j]);
    					l.add(nums[L]);
    					l.add(nums[R]);
    					
    					if(!list.contains(l)) {
    						list.add(l);
    					}
    					L++;
    					R--;
    				}
    				else if (value<target) {
    					L++;
    				}else {
    					R--;
    				}
    			}
    		}
    	}
    	
    	
		return list;
        
    }

}