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# 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

Given nums =`[1,1,2,45,46,46]`, target =`47`\
return`2`

1 + 46 = 47\
2 + 45 = 47

## Note

这里关键是去重！

```java
while (left < right && nums[left] == nums[left - 1]) { left++; }
while (left < right && nums[right] == nums[right + 1]) { right--; }
```

## Code

```java
public class Solution {
    /**
     * @param nums: an array of integer
     * @param target: An integer
     * @return: An integer
     */
    public int twoSum6(int[] nums, int target) {
        // write your code here
        if (nums == null || nums.length < 2) {
            return 0;
        }

        Arrays.sort(nums);
        int res = 0;
        int left = 0, right = nums.length - 1;
        while (left < right) {
            int sum = nums[left] + nums[right];
            if (sum == target) {
                res++;
                left++;
                right--;
                while (left < right && nums[left] == nums[left - 1]) {
                    left++;
                }
                while (left < right && nums[right] == nums[right + 1]) {
                    right--;
                }
            } else if (sum > target) {
                right--;
            } else {
                left++;
            }
        }
        return res;
    }
}
```