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Solution.java
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70 lines (65 loc) · 1.83 KB
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package ThreeSum;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
* User: Danyang
* Date: 1/17/2015
* Time: 13:10
*
* 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:
Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
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)
*/
public class Solution {
/**
* Two Pointers
* You need to ask a lots of questions
* Notice:
* 1. jump
* 2. don't box num
*
* @param num
* @return
*/
public List<List<Integer>> threeSum(int[] num) {
List<List<Integer>> ret = new ArrayList<>();
Arrays.sort(num);
int n = num.length;
for(int i=0; i<n-2; ) {
int j = i+1;
int k = n-1;
while(j<k) {
int sum = num[i]+num[j]+num[k];
if(sum==0) {
ret.add(Arrays.asList(num[i], num[j], num[k]));
k--;
j++;
// while(k>=0&&A.get(k)==A.get(k+1))
while(j<k && num[k]==num[k+1])
k--;
// while(j<=n-1&&A.get(j)==A.get(j-1))
while(j<k && num[j]==num[j-1])
j++;
}
else if(sum>0)
k--;
else
j++;
}
i++;
while(i<n-2 && num[i]==num[i-1])
i++;
}
return ret;
}
public static void main(String[] args) {
System.out.println(new Solution().threeSum(new int[]{-1, 0, 1}));
}
}