Two Sum - Unique Pairs

Given an array of integers, find how many unique pairs in the array such that their sum is equal to a specific target number. Please return the number of pairs.

Example

Example 1:

Input: nums = [1,1,2,45,46,46], target = 47 
Output: 2
Explanation:

1 + 46 = 47
2 + 45 = 47

Example 2:

Input: nums = [1,1], target = 2 
Output: 1
Explanation:
1 + 1 = 2

思路：同向双指针，注意去重复，i，nums[i]== nums[i-1] ，j nums[j] == nums[j+1]; 

public class Solution {
    /**
     * @param nums: an array of integer
     * @param target: An integer
     * @return: An integer
     */
    public int twoSum6(int[] nums, int target) {
        if(nums == null || nums.length == 0) {
            return 0;
        }
        
        Arrays.sort(nums);
        int count = 0;
        int i = 0; int j = nums.length -1;
        while(i < j) {
            int sum = nums[i] + nums[j];
            if(sum == target) {
                count++;
                i++;
                j--;
                
                while(i < j && nums[i] == nums[i-1]) {
                    i++;
                }
                while(i < j && nums[j] == nums[j+1]) {
                    j--;
                }
            } else if(sum > target){
                j--;
            } else { // sum < target;
                i++;
            }
        }
        return count;
    }
}