Apr 15

Author: siddydutta

2025-04-April-LeetCoding-Challenge/Count Good Triplets in an Array.py

@@ -0,0 +1,52 @@
+class BIT:
+    def __init__(self, size: int) -> None:
+        self.tree = [0] * (size + 1)
+
+    def update(self, i: int, delta: int) -> None:
+        i += 1
+        while i < len(self.tree):
+            self.tree[i] += delta
+            i += i & -i
+
+    def query(self, i: int) -> int:
+        res = 0
+        i += 1
+        while i > 0:
+            res += self.tree[i]
+            i -= i & -i
+        return res
+
+
+class Solution:
+    def goodTriplets(self, nums1: list[int], nums2: list[int]) -> int:
+        n = len(nums1)
+        pos2 = {num: idx for idx, num in enumerate(nums2)}
+        left, right = [0] * n, [0] * n
+
+        bit = BIT(n)
+        for y in nums1:
+            j = pos2[y]
+            left[y] = bit.query(j - 1)
+            bit.update(j, 1)
+
+        bit = BIT(n)
+        for y in reversed(nums1):
+            j = pos2[y]
+            right[y] = bit.query(n - 1) - bit.query(j)
+            bit.update(j, 1)
+
+        return sum(l * r for l, r in zip(left, right))
+
+
+def main():
+    nums1 = [2, 0, 1, 3]
+    nums2 = [0, 1, 2, 3]
+    assert Solution().goodTriplets(nums1, nums2) == 1
+
+    nums1 = [4, 0, 1, 3, 2]
+    nums2 = [4, 1, 0, 2, 3]
+    assert Solution().goodTriplets(nums1, nums2) == 4
+
+
+if __name__ == '__main__':
+    main()

2025-04-April-LeetCoding-Challenge/README.md

@@ -18,7 +18,7 @@
 | April 12 | [3272. Find the Count of Good Integers](https://leetcode.com/problems/find-the-count-of-good-integers/) | Hard | Unsolved |
 | April 13 | [1922. Count Good Numbers](https://leetcode.com/problems/count-good-numbers/) | Medium | Unsolved |
 | April 14 | [1534. Count Good Triplets](https://leetcode.com/problems/count-good-triplets/) | Easy | Solved |
-| April 15 | []() |  |  |
+| April 15 | [2179. Count Good Triplets in an Array](https://leetcode.com/problems/count-good-triplets-in-an-array/) | Hard | Unsolved |
 | April 16 | []() |  |  |
 | April 17 | []() |  |  |
 | April 18 | []() |  |  |
@@ -41,4 +41,4 @@
 | ---    | --- | --- | --- |
 | Easy   | 5 | 5 | 0 |
 | Medium | 7 | 5 | 2 |
-| Hard   | 2 | 0 | 2 |
+| Hard   | 3 | 0 | 3 |