Given an array S of n integers, are there elements a, b, c in S 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.
For example, given array S = [-1, 0, 1, 2, -1, -4], A solution set is: [ [-1, 0, 1], [-1, -1, 2] ]
tag : two pointers
public class Solution {
public List<List<Integer>> threeSum(int[] nums) {
List<List<Integer>> result = new ArrayList<List<Integer>>();
if(nums == null || nums.length < 3){
return result;
}
Arrays.sort(nums);
for(int i = 0 ; i < nums.length - 2; i++){
int a = nums[i];
if(i != 0 && nums[i-1] == nums[i]){
continue;
}
int left = i + 1;
int right = nums.length - 1;
while(left < right){
int b = nums[left];
int c = nums[right];
int sum = a + b + c;
if(sum == 0){
List<Integer> tmp = new ArrayList<Integer>();
tmp.add(a);
tmp.add(b);
tmp.add(c);
result.add(tmp);
left++;
right--;
while(left < right && nums[left] == nums[left-1]){
left ++;
}
while(left < right && nums[right + 1] == nums[right]){
right --;
}
}else if(a + b + c < 0){
left ++;
}else{
right --;
}
}
}
return result;
}
}
原文：http://www.cnblogs.com/superzhaochao/p/6399094.html