923

Author: ProHiryu

code/923.3-sum-with-multiplicity.py

@@ -0,0 +1,22 @@
+#
+# @lc app=leetcode id=923 lang=python3
+#
+# [923] 3Sum With Multiplicity
+#
+
+# @lc code=start
+class Solution:
+    def threeSumMulti(self, arr: List[int], target: int) -> int:
+        cnt, ans = collections.Counter(arr), 0
+        for i in cnt:
+            for j in cnt:
+                k = target - i - j
+                if i == j == k:
+                    ans += cnt[i] * (cnt[i] - 1) * (cnt[i] - 2) // 6
+                elif i == j:
+                    ans += cnt[i] * (cnt[i] - 1) // 2 * cnt[k]
+                elif i < j < k:
+                    ans += cnt[i] * cnt[j] * cnt[k]
+        return ans % (10**9 + 7)
+# @lc code=end
+