publicList<List<Integer>>fourSum(int[] num, inttarget) {
Arrays.sort(num);
List<List<Integer>>res=newLinkedList<>();
//多加了层循环for (intj=0; j<num.length-3; j++) {
//防止重复的if (j==0|| (j>0&&num[j] !=num[j-1]))
for (inti=j+1; i<num.length-2; i++) {
//防止重复的，不再是 i == 0 ，因为 i 从 j + 1 开始if (i==j+1||num[i] !=num[i-1]) {
intlo=i+1, hi=num.length-1, sum=target-num[j] -num[i];
while (lo<hi) {
if (num[lo] +num[hi] ==sum) {
res.add(Arrays.asList(num[j], num[i], num[lo], num[hi]));
while (lo<hi&&num[lo] ==num[lo+1])
lo++;
while (lo<hi&&num[hi] ==num[hi-1])
hi--;
lo++;
hi--;
                        } elseif (num[lo] +num[hi] <sum)
lo++;
elsehi--;
                    }
                }
            }
    }
returnres;
}