/**18. 4Sum
* @param nums
* @param target
* @return 4个数之和为target
*/
public List<List<Integer>>
fourSum(
int[] nums,
int target) {
List<List<Integer>> list =
new ArrayList<List<Integer>>();
HashSet<List<Integer>> set =
new HashSet<List<Integer>>();
Arrays.sort(nums);
for (
int i=
0, len=nums.length; i<len-
4; i++) {
for (
int j=i+
1; j<len-
3; j++) {
int low = j+
1;
int high = len-
1;
while (low < high) {
int sum = nums[i] + nums[j] + nums[low] + nums[high];
if (sum == target) {
List<Integer> item =
new ArrayList<Integer>();
item.add(nums[i]);
item.add(nums[j]);
item.add(nums[low]);
item.add(nums[high]);
if (!set.contains(item)) {
set.add(item);
list.add(item);
}
low++;
high--;
}
else if(sum < target) {
low++;
}
else {
high--;
}
}
}
}
return list;
}
注意：找到item之后更改指针位置哦
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