added Two Sum - Unique Pairs

Author: minhyeong-joe

Array/TwoSumUniquePairs/README.md

@@ -0,0 +1,31 @@
+# Two Sum - Unique Pairs
+
+[Leetcode Link](https://leetcode.com/discuss/interview-question/372434)
+
+## Problem:
+
+Given an int array nums and an int target, find how many unique pairs in the array such that their sum is equal to target. Return the number of pairs.
+
+## Example:
+
+```
+Input: nums = [1, 1, 2, 45, 46, 46], target = 47
+Output: 2
+Explanation:
+1 + 46 = 47
+2 + 45 = 47
+```
+
+```
+Input: nums = [1, 1], target = 2
+Output: 1
+Explanation:
+1 + 1 = 2
+```
+
+```
+Input: nums = [1, 5, 1, 5], target = 6
+Output: 1
+Explanation:
+[1, 5] and [5, 1] are considered the same.
+```

Array/TwoSumUniquePairs/solution.py

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+def uniqueTwoSum(nums, target):
+    numPairs = 0
+    # sort array
+    nums.sort()
+    # two pointers from left-end and right-end
+    left = 0
+    right = len(nums)-1
+    while left < right:
+        # skip the same numbers (finding UNIQUE pairs)
+        while left >= 1 and nums[left] == nums[left-1]:
+            left += 1
+            if left >= len(nums):
+                break
+        while right < len(nums)-1 and nums[right] == nums[right+1]:
+            right -= 1
+            if right < 0:
+                break
+        if left >= right:
+            break
+        if nums[left] + nums[right] == target:
+            numPairs += 1
+            left += 1
+            right -= 1
+        elif nums[left] + nums[right] > target:
+            right -= 1
+        else:
+            left += 1
+    return numPairs
+
+
+# simple test case
+nums = [1, 1, 2, 3, 4, 4, 43, 45, 45, 46, 46]
+target = 47
+print(uniqueTwoSum(nums, target))
+
+# all dups
+nums = [1, 1, 1, 1, 1, 1, 1]
+target = 2
+print(uniqueTwoSum(nums, target))
+
+# no two sum to target
+nums = [2, 3, 6, 2, 3]
+target = 7
+print(uniqueTwoSum(nums, target))
+
+# unique
+nums = [1, 5, 1, 5]
+target = 6
+print(uniqueTwoSum(nums, target))

README.md

@@ -48,6 +48,7 @@ Languages used: Java and Python
 - [Subarray Sum Equals K](Array/SubarraySumEqualsK)
 - [Sum Of Even Numbers After Queries](Array/SumOfEvenNumbersAfterQueries)
 - [Third Maximum Number](Array/ThirdMaximumNumber)
+- [Two Sum - Unique Pairs](Array/TwoSumUniquePairs)
 
 ### [Bit Manipulation](./BitManipulation)