java - 3SUM: avoid duplicates -

problem: given array s of n integers, there elements a, b, c in s such + b + c = 0? find unique triplets in array gives sum of zero.

to avoid duplicates use if-clause in while loop, , wondering why not work. thanks!

public list<list<integer>> threesum(int[] nums) {     list<list<integer>> result = new arraylist<list<integer>>();     arrays.sort(nums);      (int = 0; i<nums.length; i++){         if (i > 0 && nums[i] == nums[i-1]){             continue;         }         int target = -1*nums[i];         int start = i+1;         int end = nums.length-1;          while (start < end){              if (nums[start] == nums[start+1]){                 start++;             }               if (nums[end] == nums[end--]){                 end--;             }               if (nums[start]+nums[end] == target){                 system.out.printf("found");                 list<integer> temp = new arraylist<integer>();                 temp.add(nums[i]);                 temp.add(nums[start]);                 temp.add(nums[end]);                 result.add(temp);                 start++;                 end--;             } else if (nums[start]+nums[end] < target) {                 start++;             } else {                 end--;             }         }     }     return result; 

i testing on [-1,0,1] , code returned empty list. tried debug , printed messages, , seems when i=1, in while loop, first enters

if (nums[start] == nums[start+1]){                 start++; }  

but nums[start] not equal nums[start+1] when start=1. quite bizzare. can explain me?

replace string in code from

if (nums[end] == nums[end--]) { 

to

 if (nums[end] == nums[end - 1]) {