Feature/daily problem

leetcode/maximum_product_of_three_numbers/maximum_product_of_three_numbers.py

@@ -0,0 +1,33 @@
+from typing import List
+
+
+class Solution:
+    def maximumProduct(self, nums: List[int]) -> int:
+        """
+        628. Maximum Product of Three Numbers
+
+        After sorting, the max product of three numbers is the larger of:
+          1) three largest values (all positive, or least-negative if all negative)
+          2) two smallest (most negative) * largest (neg*neg*pos can dominate)
+
+        Time:  O(n log n)
+        Space: O(1) extra if sort is in-place (O(n) depending on sort impl)
+        """
+        nums.sort()
+        return max(
+            nums[-1] * nums[-2] * nums[-3],
+            nums[0] * nums[1] * nums[-1],
+        )
+
+
+if __name__ == "__main__":
+    s = Solution()
+    assert s.maximumProduct([1, 2, 3]) == 6
+    assert s.maximumProduct([1, 2, 3, 4]) == 24
+    assert s.maximumProduct([-1, -2, -3]) == -6
+    assert s.maximumProduct([-4, -3, -2, -1, 60]) == 720
+    assert s.maximumProduct([-100, -98, -1, 2, 3, 4]) == 39200
+    assert s.maximumProduct([-1, -2, 1, 2, 3]) == 6
+    assert s.maximumProduct([0, 0, 0]) == 0
+    assert s.maximumProduct([-5, 0, 1, 2]) == 0
+    print("ok")

leetcode/maximum_product_of_two_elements_in_an_array/maximum_product_of_two_elements_in_an_array.py

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+from typing import List
+
+
+class Solution:
+    def maxProduct(self, nums: List[int]) -> int:
+        # (a-1)*(b-1) is maximized by the two largest values (nums[i] >= 1).
+        max1 = max2 = 0
+        for num in nums:
+            if num > max1:
+                max2, max1 = max1, num
+            elif num > max2:
+                max2 = num
+        return (max1 - 1) * (max2 - 1)

leetcode/number_of_unique_xor_triplets_ii/number_of_unique_xor_triplets_ii.py

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+from typing import List
+
+
+class Solution:
+    def uniqueXorTriplets(self, nums: List[int]) -> int:
+        """
+        Count distinct values of nums[i] ^ nums[j] ^ nums[k] over i <= j <= k.
+
+        Key insight: index reuse (i==j or j==k) only produces values already in
+        the array. Every triple of values (a, b, c) from the distinct set U is
+        achievable, so the answer is |{a ^ b ^ c : a, b, c in U}|.
+
+        nums[i] <= 1500 => XOR results fit in [0, 2047]. Build all pairwise XORs,
+        then XOR each with every value in U.
+        """
+        # Presence of values; range is small
+        present = [False] * 2048
+        for x in nums:
+            present[x] = True
+        vals = [x for x in range(2048) if present[x]]
+
+        # All pairwise XORs a ^ b for a, b in U (includes a ^ a == 0)
+        pair = [False] * 2048
+        for i, a in enumerate(vals):
+            for b in vals[i:]:
+                pair[a ^ b] = True
+        pair_vals = [x for x in range(2048) if pair[x]]
+
+        # All triple XORs (a ^ b) ^ c
+        trip = [False] * 2048
+        for p in pair_vals:
+            for c in vals:
+                trip[p ^ c] = True
+
+        return sum(trip)

leetcode/shift_2d_grid/shift_2d_grid.py

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+from typing import List
+
+
+class Solution:
+    def shiftGrid(self, grid: List[List[int]], k: int) -> List[List[int]]:
+        """
+        1260. Shift 2D Grid
+
+        Treat the m x n grid as a flattened 1D array of length m*n.
+        One shift is a right-rotate by 1 in that array (last -> first).
+        After k shifts, element at flat index i moves to (i + k) % (m*n).
+
+        Time:  O(m * n)
+        Space: O(m * n) for the result
+        """
+        m, n = len(grid), len(grid[0])
+        total = m * n
+        k %= total
+        ans = [[0] * n for _ in range(m)]
+        for i in range(m):
+            for j in range(n):
+                ni, nj = divmod((i * n + j + k) % total, n)
+                ans[ni][nj] = grid[i][j]
+        return ans
+
+
+if __name__ == "__main__":
+    s = Solution()
+    assert s.shiftGrid([[1, 2, 3], [4, 5, 6], [7, 8, 9]], 1) == [
+        [9, 1, 2],
+        [3, 4, 5],
+        [6, 7, 8],
+    ]
+    assert s.shiftGrid([[3, 8, 1, 9], [19, 7, 2, 5], [4, 6, 11, 10], [12, 0, 21, 13]], 4) == [
+        [12, 0, 21, 13],
+        [3, 8, 1, 9],
+        [19, 7, 2, 5],
+        [4, 6, 11, 10],
+    ]
+    assert s.shiftGrid([[1, 2, 3], [4, 5, 6], [7, 8, 9]], 9) == [
+        [1, 2, 3],
+        [4, 5, 6],
+        [7, 8, 9],
+    ]
+    assert s.shiftGrid([[1], [2], [3], [4], [5], [6], [7]], 23) == [
+        [6],
+        [7],
+        [1],
+        [2],
+        [3],
+        [4],
+        [5],
+    ]
+    print("ok")