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62 lines (56 loc) · 1.61 KB
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/*
15. 3Sum
Medium
Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
Note:
The solution set must not contain duplicate triplets.
Example:
Given array nums = [-1, 0, 1, 2, -1, -4],
A solution set is:
[
[-1, 0, 1],
[-1, -1, 2]
]
*/
package twopointers;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class ThreeSum {
public static List<List<Integer>> threeSum(int[] nums) {
if (nums == null || nums.length < 3) {
return null;
}
Arrays.sort(nums);
List<List<Integer>> result = new ArrayList<>();
for (int i = 0; i < nums.length - 2; i++) {
//去重复
if (i > 0 && nums[i] == nums[i - 1]) {
continue;
}
int l = i + 1;
int r = nums.length - 1;
int target = -nums[i];
while (l < r) {
int sum = nums[l] + nums[r];
if (sum == target) {
result.add(Arrays.asList(nums[i], nums[l], nums[r]));
//去重复
while (l < r && nums[l] == nums[l + 1]) {
l++;
}
while (l < r && nums[r] == nums[r - 1]) {
r--;
}
l++;
r--;
} else if (sum > target) {
r--;
} else {
l++;
}
}
}
return result;
}
}