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imsosleepy.java
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55 lines (48 loc) ยท 1.85 KB
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// ํฌํฌ์ธํฐ ๋ฐฉ์์ผ๋ก ๊ตฌํ
// ํฌํฌ์ธํฐ์ ๊ธฐ๋ณธ ์๊ฐ๋ณต์ก๋๊ฐ O(2^n)์ด๋ฏ๋ก ์ค๋ฆ์ฐจ์์ผ๋ก ์ ๋ ฌํ๋ O(NlogN)์ ๋ง์๊ป ์ฌ์ฉํด๋ ๋๋ค.
public List<List<Integer>> threeSum(int[] nums) {
List<List<Integer>> result = new ArrayList<>();
Arrays.sort(nums);
for(int i =0; i< nums.length-2;i++) {
if (i > 0 && nums[i] == nums[i - 1]) continue;
int left = i + 1, right = nums.length - 1;
while (left < right) {
int sum = nums[i] + nums[left] + nums[right];
if (sum == 0) {
result.add(Arrays.asList(nums[i], nums[left], nums[right]));
while (left < right && nums[left] == nums[left + 1]) left++;
while (left < right && nums[right] == nums[right - 1]) right--;
left++;
right--;
} else if (sum < 0) {
left++;
} else {
right--;
}
}
}
return result;
}
// dfs ํ์ด๋ฅผ ์๊ฐํ์ผ๋ dfs ๋ฐฉ์์ ๋ฌด์กฐ๊ฑด O(2^n)์ ๊ฒฐ๊ณผ๊ฐ ๋์จ๋ค.
// ํ์ ์์ ์ค๋ต
public class Solution {
public List<List<Integer>> threeSum(int[] nums) {
Set<List<Integer>> answerSet = new HashSet<>();
nums = Arrays.stream(nums).sorted().toArray();
dfs(nums, 0, new ArrayList<>(), answerSet);
return new ArrayList<>(answerSet);
}
public void dfs(int[] nums, int index, List<Integer> temp, Set<List<Integer>> answerSet) {
if (temp.size() == 3) {
int result = 0;
for (int element : temp) result += element;
if (result == 0) answerSet.add(new ArrayList<>(temp));
return;
}
for (int i = index; i < nums.length; i++) {
temp.add(nums[i]);
dfs(nums, i + 1, temp, answerSet);
temp.remove(temp.size() - 1);
}
}
}