3sum in python

Python/923-3Sum With Multiplicity.py

@@ -0,0 +1,44 @@
+# Link to problem: https://leetcode.com/problems/3sum-with-multiplicity/
+
+# Given an integer array arr, and an integer target, return the number of tuples i, j, k such that i < j < k and arr[i] + arr[j] + arr[k] == target.
+
+class Solution:
+    def threeSumMulti(self, arr: List[int], target: int) -> int:
+        N=len(arr)
+        arr.sort()
+        ans=0
+        for i in range(N):
+            T=target-arr[i]
+            j=i+1 ; k=N-1
+            while k > j:
+                if arr[k]+arr[j]<T:
+                    j+=1
+                elif arr[k]+arr[j]>T:
+                    k-=1
+                else:
+                    if arr[j]==arr[k]:
+                        total=k-j+1
+                        ans+=total*(total-1)//2
+                        ans%=(int(1e9)+7)
+                        break
+                    else:
+                        cnt1=0
+                        cnt2=0
+                        st=arr[j];en=arr[k]
+                        while arr[j]==st:
+                            cnt1+=1
+                            j+=1
+                        while arr[k]==en:
+                            cnt2+=1
+                            k-=1
+                        ans+=cnt1*cnt2
+                        ans%=(int(1e9)+7)
+        return ans%(int(1e9)+7)
+
+'''
+Input: arr = [1,1,2,2,3,3,4,4,5,5], target = 8
+Output: 20
+
+Input: arr = [1,1,2,2,2,2], target = 5
+Output: 12
+'''